## Thursday, December 31, 2009

### Interesting Astrophysics: Dec 21 to Dec 31, 2009

The final edition of Interesting Astrophysics for 2009 is as diverse as ever. Of particular note, a classic superwind in the "8 o'clock arc" at z~2.7 (Dessauges-Zavadsky et al), a sample of galaxy groups analogous to our own Local Group (Marino et al), stellar wind mass loss rates in hot stars (Lucy et al), and astrobiology (Cirkovic et al).

Galaxies and Starbursts

Galaxy Evolution in Local Group Analogs. I. A GALEX study of nearby groups
A. Marino, L. Bianchi, R. Rampazzo, L.M. Buson, D. Bettoni,
Comments: 20 pages, 13 figures, accepted for publication in Astronomy and Astrophysics

Rest-frame ultraviolet spectrum of the gravitationally lensed galaxy the 8 o'clock arc': stellar and interstellar medium properties
M. Dessauges-Zavadsky, S. D'Odorico, D. Schaerer, A. Modigliani, C. Tapken, J. Vernet,
Comments: 17 pages, 10 figures, A&amp;A, accepted

From their abstract: "We present the first detailed analysis of the rest-frame UV spectrum of the gravitationally lensed Lyman break galaxy (LBG), the 8 o'clock arc'. The spectrum of the 8 o'clock arc is rich in stellar and interstellar medium (ISM) features, and presents several similarities to the well-known MS1512-cB58 LBG. ... The ISM lines extend over ~1000 km/s and have their peak optical depth blueshifted relative to the stars, implying gas outflows of about -120 km/s. The Ly-alpha line is dominated by a damped absorption profile on top of which is superposed a weak emission, redshifted relative to the ISM lines by about +690 km/s and resulting from multiply backscattered Ly-alpha photons emitted in the HII region surrounded by the cold, expanding ISM shell."

Luminosity-Metallicity Relations for Blue Compact Dwarf Galaxies in the Optical and Near-Infrared
Yinghe Zhao, Yu Gao, Qiusheng Gu,
Comments: 32 pages, 7 figures, accepted for publication in the Astrophysical Journal

Black Holes and AGN

Infrared Diagnostics for the Extended 12 micron Sample of Seyferts
Stefi A. Baum, Jack F. Gallimore, Christopher P. O'Dea, Catherine L. Buchanan, Jacob Noel-Storr, David J. Axon, Andy Robinson, Moshe Elitzur, Meghan Dorn, Shawn Staudaher, Martin Elvis,

Note to self: this paper deals with the correlations within the sample, but does not name the individual members of the sample.

Numerical Astrophysics and Hydrodynamics

Kristopher Yirak, Adam Frank, Andrew J. Cunningham,
Comments: 24 pages, 7 figures. Submitted to the Astrophysical Journal

They find that a fixed number of cells per radius does not lead to convergence in simulations of radiatively cooling clumps. They present alternative prescriptions for assessing numerical convergence.

X-ray astronomy

A wide field X-ray telescope for astronomical survey purposes: from theory to practice
P. Conconi, S. Campana, G. Tagliaferri, G. Pareschi, O. Citterio, V. Cotroneo, L. Proserpio, M. Civitani,

Stars, Supernovae and Planets

Mass fluxes for hot stars
L.B. Lucy,
Comments: Submitted to A&amp;A; 6 pages, 5 figures; second revision

Comprehensive Photometric Histories of All Known Galactic Recurrent Novae
Comments: ApJSupp in press, 273 pages, 34 tables, 71 figures

Note the size of the paper! That is definitely a labor of love.

3D simulations of supernova remnants evolution including non-linear particle acceleration
Gilles Ferrand, Anne Decourchelle, Jean Ballet, Romain Teyssier, Federico Fraschetti,
Comments: accepted for publication in A&A (final version)

PopStar Evolutionary Synthesis Models II: Optical emission-line spectra from Giant Hii regions
M.L. Martín-Manjón, M.L. García-Vargas, M. Mollá, A.I. Díaz,
Comments: 20 pages, 26 figures, accepted for publication in MNRAS Main Journal

Including All the Lines
Robert L. Kurucz,
Comments: 9 pages, no figures. Presented at "Dimitrifest" conference in Boulder, Colorado, March 30 - April 3, 2009
Journal-ref: Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics. Edited by I. Hubeny, J.M. Stone, K. MacGregor, and K. Werner. AIP Conference Proceedings 1171, pp. 43-51, 2009

Astrobiology

Galactic Punctuated Equilibrium: How to Undermine Carter's Anthropic Argument in Astrobiology
Milan M. Cirkovic, Branislav Vukotic, Ivana Dragicevic,
Journal-ref: Published in Astrobiology, 2009, Volume 9, Issue 5, pp. 491-501

## Tuesday, December 29, 2009

### Where is the joy in research?

Dennis Overbye has a rather odd essay in the NYT: "The Joy of Physics Isn’t in the Results, but in the Search Itself ." It starts off reading as a conventional justification for pure research based on the unanticipated but fundamentally useful technological products it produces, products that applied scientific or technological research would not have produced. You know the things: hypertext and the WWW, digital camera sensors, MRI and PET scanners, Velcro, pens that write when upside down, memory foam beds.

But then it veers off to tackle, as far as I can tell, the slow and bumpy road along the path of scientific progress from Overbye's perspective as a science writer in 2009. The pre-servicing mission Hubble contrasted with post servicing mission glory, the Large Hadron Collider's commissioning woes, and the pre-announcement hype of CDMS-2's decidedly ambiguous one (or two, if you're generous) sigma pseudo result. This is more in line with the essay's title.

I presume that Overbye's point was to highlight that the scientific method is not all about predictable results that appear in a regular and preplanned way. That both the results and process of science are unpredictable, and that's where the "joy" of it lies.

Its all very well, admirable even, for a science writer to tackle societies naive and preconceived views of how science works, but I must say I think Overbye's essay veers to much in the opposite direction to ignore the many years of routine operation by telescopes (the result of careful planning and hard work) and particle colliders, where experiments are planned and go roughly as expected. Unanticipated surprises happen, but the surprise us because they're rare and contrast so vividly with the larger edifice of scientific progress built slow accumulation and refinement.

Returning to the title of Overbye essay, I'd agree that doing science is fun. Seeing or discovering things that no-one else has ever seen or thought is a thrill. The mental challenge itself is pleasurable, even when you're treading scientific ground where others have gone before. But getting a result - answering a question - even if it isn't the answer you expected, is the payoff and culmination of all the hard work. So some of the joy of physics is certainly in the search, but a lot of it is in getting results.

## Friday, December 18, 2009

### CDMS-2's 1-sigma dark matter result.

After much speculation the CDMS-2 "dark matter detection result" announced yesterday turns out to be 2 events with an expected background rate of 0.8 events in the 2007-2008 time frame of the experiment (SciAm news piece).

Exactly two events would happen by chance ~14% of the time (>=2 events would happen 20% of the time), so we're basically talking about a ~1 sigma result. Meh. Hardly impressive. It'd take 10 events under a 0.8 count background rate to get me excited.

### Interesting Astrophysics: Dec 07 to 18

Not a white christmas but a windy one: Razoumov, Westmoquette et al, Rubin et al, Vanzella et al, Crenshaw et al, and Kobulnicky et al are all wind-related papers or preprints (and mainly on galactic winds). Another paper of particular note is Welsh et al's amazing 3-D mapping of the local neutral ISM (within 300 pc) using NaI and CaII absorption line spectroscopy toward 1857 nearby early-type stars.

Galaxies and Starbursts

Damped Lyα Absorber Kinematics and Outflows from Starburst Galaxies
Razoumov, Alexei O., 2009, The Astrophysical Journal, Volume 707, Issue 1, pp. 738-749.
PDF (1.84 MB) | HTML

VLT/FLAMES-ARGUS observations of stellar wind-ISM cloud interactions in NGC 6357
Westmoquette, M. S.; Slavin, J. D.; Smith, L. J.; Gallagher, J. S., III, 2009, MNRAS, in press
Full Text: HTML, PDF (Size: 2563K)

PAH processing in a hot gas
E. R. Micelotta, A. P. Jones, A. G. G. M. Tielens,
Comments: 16 pages, 11 figures, accepted for publication in Astronomy and Astrophysics

From their abstract: "The PAH lifetime in a tenuous hot gas (n_H ~ 0.01 cm^-3, T ~ 10^7 K), typical of the coronal gas in galactic outflows, is found to be about thousand years, orders of magnitude shorter than the typical lifetime of such objects. Conclusions: In a hot gas, PAHs are principally destroyed by electron collisions and not by the absorption of X-ray photons from the hot gas. The resulting erosion of PAHs occurs via C_2 loss from the periphery of the molecule, thus preserving the aromatic structure. The observation of PAH emission from a million degree, or more, gas is only possible if the emitting PAHs are ablated from dense, entrained clumps that have not yet been exposed to the full effect of the hot gas."

The Persistence of Cool Galactic Winds in High Stellar Mass Galaxies Between z~1.4 and ~1
Kate H. R. Rubin, Benjamin J. Weiner, David C. Koo, Crystal L. Martin, J. Xavier Prochaska, Alison L. Coil, Jeffrey A. Newman,
Comments: Submitted to ApJ. 25 pages, 19 figures, Figure 2 reduced in resolution. Uses emulateapj format

From their abstract: "We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption line profiles in coadded spectra of 468 galaxies at 0.7 < z < 1.5. ... The outflows
have hydrogen column densities N(H) > 10^19.3 cm^-2, and extend to velocities
of ~500 km/s. While galaxies with SFR > 10 Msun/yr host strong outflows in both
this and the W09 sample, we do not detect outflows in lower-SFR (i.e., log
M_*/Msun < 10.5) galaxies at lower redshifts. Using a simple galaxy evolution
model which assumes exponentially declining SFRs, we infer that strong outflows
persist in galaxies with log M_*/Msun > 10.5 as they age between z=1.4 and z~1,
presumably because of their high absolute SFRs. Finally, using high resolution
HST/ACS imaging in tandem with our spectral analysis, we find evidence for a
weak trend (at 1 sigma significance) of increasing outflow absorption strength
with increasing galaxy SFR surface density."

The unusual NIV]-emitter galaxy GDS J033218.92-275302.7: star formation or AGN-driven winds from a massive galaxy at z=5.56
E. Vanzella, A. Grazian, M. Hayes, L. Pentericci, D. Schaerer, M. Dickinson, S. Cristiani, M. Giavalisco, A. Verhamme, M. Nonino, P. Rosati,
Comments: 13 pages, 9 figures. Accepted for publication in Astronomy and Astrophysics

The central energy source of 70micron-selected galaxies: Starburst or AGN?
M. Symeonidis, D. Rosario, A. Georgakakis, J. Harker, E. S. Laird, M. J. Page
Comments: 20 pages, 14 figures, accepted for publication in MNRAS

It is starbursts.

Model analysis of the very high energy detections of the starburst galaxies M82 and NGC 253
E. de Cea del Pozo, D. F. Torres, A. Y. Rodriguez, O. Reimer,
Comments: 6 pages, 3 figures, 2 tables, 2009 Fermi Symposium, eConf Proceedings C091122

Black Holes and AGN

The Geometry of Mass Outflows and Fueling Flows in the Seyfert 2 Galaxy Mrk 3
D.M. Crenshaw, S.B. Kraemer, H.R. Schmitt, Y.L. Jaffe, R.P. Deo, N.R. Collins, T.C. Fischer,
Comments: 22 page, 7 figures, accepted for publication in the Astronomical Journal

Their abstract: We present a study of the resolved emission-line regions and an inner dust/gas disk in the Seyfert 2 galaxy Mrk 3, based on Hubble Space Telescope observations. We show that the extended narrow-line region (ENLR), spanning ~4 kpc, is defined by the intersection of the ionizing bicone of radiation from the AGN and the inner disk, which is not coplanar with the large-scale stellar disk. This intersection leads to different position and opening angles of the ENLR compared to the narrow-line region (NLR). A number of emission-line arcs in the ENLR appear to be continuations of dust lanes in the disk, supporting this geometry. The NLR, which consists of outflowing emission-line knots spanning the central ~650 pc, is in the shape of a backwards S. This shape may arise from rotation of the gas, or it may trace the original fueling flow close to the nucleus that was ionized after the AGN turned on."

Stars, Supernovae and Planets

OB Stars & Stellar Bowshocks in Cygnus-X: A Novel Laboratory Estimating Stellar Mass Loss Rates
Henry A. Kobulnicky, Ian J. Gilbert, Daniel C. Kiminki, Comments: 49 pages, 19 figures; Accepted for publication in ApJ; full-resolution color figure version available at this http URL; comments invited

CoRoT-7 b: Super-Earth or Super-Io?
Rory Barnes, Sean N. Raymond, Richard Greenberg, Brian Jackson, Nathan A. Kaib,
Comments: 13 pages, 3 figures, accepted to ApJ Letters

The simultaneous formation of massive stars and stellar clusters
Rowan J. Smith, Steven Longmore and Ian Bonnell, 2009, MNRAS, 400, 1775
Full Text: HTML, PDF (Size: 20619K)

Updated stellar yields from Asymptotic Giant Branch models
Amanda I. Karakas,
Comments: Accepted for publication in MNRAS; 15 pages

New 3-D gas density maps of NaI and CaII interstellar absorption within 300pc
Barry Y. Welsh, Rosine Lallement, Jean-Luc Vergely, Severine Raimond,

The NaI and CaII distributions are quite different. A very impressive piece of work.

Numerical Methods and Theoretical Astrophysics

Astrophysical turbulence
Axel Brandenburg, Aake Nordlund,
Comments: 80 pages, 24 figures, submitted to Reports on Progress in Physics. For higher figure quality and more frequent revisions see this http URL

Detailed Decomposition of Galaxy Images. II. Beyond Axisymmetric Models
Chien Y. Peng, Luis C. Ho, Chris D. Impey, Hans-Walter Rix,
Comments: 41 pages, 22 figures, AJ submitted. Comments welcomed. Full resolution version of this paper is available at: this http URL

Dynamical Models for the Formation of Elephant Trunks in H II Regions
Jonathan Mackey, Andrew J. Lim,
Comments: 19 pages, 11 figures, accepted for publication in MNRAS. Version with high resolution figures available at this http URL

## Tuesday, December 15, 2009

### XMM-Newton AO-9 accepted proposals announced

Speaking of XMM-Newton, the results of AO-9 observing proposal round have just been made available.

The list of XMM-Newton proposals accepted by the AO-9 Observing Time
Allocation Committee (OTAC) and associated proposal abstracts are
available at:

http://xmm.esac.esa.int/external/xmm_news/otac_results/ao9_results/

The Principal Investigators of submitted proposals have been informed
about the results of the OTAC evaluation by e-mail. The e-mail
contains the details about the second phase proposal submission for
successful observations, which will need to be done via the XMM-Newton
Remote Proposal Submission System (XRPS). The XRPS will be closed on
the 5th of February 2010 at 13:00 UT.

AO-9 observations will start to be routinely performed in May 2010.

## Thursday, December 10, 2009

### Happy 10th birthday, XMM-Newton

From the XMM-Newton mailing list:

10 Years in Orbit: HAPPY BIRTHDAY, XMM-Newton!

Today, XMM-Newton is celebrating its 10th anniversary. On the 10th of
December 1999 at 14:32 GMT the European Space Agency's XMM-Newton
observatory was launched and started exploring the wonders of the
X-ray universe.

During its first decade of operations, XMM-Newton has supplied new
data to every aspect of astronomy, improving our understanding from
nearby comets to the most distant quasars and gamma-ray bursts.

A dedicated web site celebrating this event is available at:

http://xmm.esac.esa.int/external/xmm_news/items/10th_Anniversary/

We wish all the best to XMM-Newton for the years to come.

We take this opportunity to thank you all for your continued support
and interest in the mission.

The ESA website for XMM-Newton produced the highlights poster shown above (higher resolution versions available here). Of course M82, everyone's favorite starburst galaxy with a galactic wind, features prominently.

## Friday, December 04, 2009

### Interesting Astrophysics: Nov 23 to Dec 04, 2009

In honor of the Thanksgiving Day Holiday here in the US the preprint server has produced a veritable feast of interesting papers over the last two weeks.

Of particular note are the following.

Radio spectra of everyone's favorite starbursts galaxies: M82, NGC 253 and Arp 220 (Williams & Bower). Cosmological N-body/SPH simulations affirming the importance of galactic winds, only not quite in the normal way (Oppenheimer et al).

An apparently physically large (6+ kpc) and powerful wind in the AGN SDSS J0318-0600 (Dunn et al), but note that... Krug et al find that AGN probably do not play a significant role in driving the outflows from most Seyfert galaxies, except possibly the high velocity outflows in some Seyfert 1s. Camus et al and Falceta-Goncalves et al have interesting, but very different, simulations of filamentary structures in the Crab Nebula and NGC 1275 respectively (The HST press release image of NGC 1275 [Fabian et al] is shown above).

Sadakane et al find high velocity narrow Na I absorption lines in the spectrum of Nova V1280 Sco. Bowler et al find that massive planets appear significantly more common around A stars than G stars.

Galaxies and Starbursts

The properties of the stellar populations in ULIRGs II: the star formation histories and evolution
Comments: Accepted for publication in MNRAS. The paper contains 16 pages, 6 figures and 7 tables

GALEX Ultraviolet Imaging of Dwarf Galaxies and Star Formation
Deidre A. Hunter, Bruce G. Elmegreen, Bonnie C. Ludka,
Comments: 28 pages, 22 figures, 7 tables, to be published in Astronomical Journal

Forty Years of Research on Isolated Galaxies
J. W. Sulentic,
Comments: 8 pages - to appear in the proceedings of 'Galaxies in Isolation: Exploring Nature vs. Nurture', held in Granada, Spain 12-15 May 2009. Editors: L. Verdes-Montenegro, A. del Olmo and J. Sulentic. PASP Conference Series

Evaluating the Calorimeter Model with Broadband, Continuous Spectra of Starburst Galaxies Observed with the Allen Telescope Array
Peter K. G. Williams, Geoffrey C. Bower,
Comments: 44 pages, 15 figures, ApJ accepted

Their abstract: "Although the relationship between the far-infrared and cm-wave radio luminosities of normal galaxies is one of the most striking correlations in astronomy, a solid understanding of its physical basis is lacking. In one interpretation, the "calorimeter model," rapid synchrotron cooling of cosmic ray electrons is essential in reproducing the observed linear relationship. Observed radio spectra, however, are shallower than what is expected of cooled synchrotron emission. In Thompson et al. (2006), a simple parameterized model is presented to explain how relatively shallow observed spectra might arise even in the presence of rapid synchrotron cooling by accounting for ionization losses and other cooling mechanisms. During the commissioning of the 42-element Allen Telescope Array, we observed the starburst galaxies M82, NGC 253, and Arp 220 at frequencies ranging from 1 to 7 GHz, obtaining unprecedented broadband continuous radio spectra of these sources. We combine our observations with high-frequency data from the literature to separate the spectra into thermal and nonthermal components. The nonthermal components all steepen in the cm-wave regime and cannot be well-modeled as simple power laws. The model of Thompson et al. is consistent with our M82 results when plausible parameters are chosen, and our results in fact significantly shrink the space of allowed model parameters. The model is only marginally consistent with our NGC 253 data. Assuming the Thompson et al. model, a steep electron energy injection index of p = -2.5 is ruled out in M82 and NGC 253 to >99% confidence. We describe in detail the observing procedures, calibration methods, analysis, and consistency checks used for broadband spectral observations with the Allen Telescope Array."

Feedback and Recycled Wind Accretion: Assembling the z=0 Galaxy Mass Function
Benjamin D. Oppenheimer, Romeel Davé, Dušan Kereš, Mark Fardal, Neal Katz, Juna A. Kollmeier, David H. Weinberg,
Comments: 15 pages, 6 figures, submitted to MNRAS

Black Holes & AGN

The Quasar Outflow Contribution to AGN Feedback: VLT Measurements of SDSS J0318-0600
Jay P. Dunn, Manuel A. Bautista, Nahum Arav, Maxwell Moe, Kirk T. Korista, Elisa Costantini, Chris Benn, Sara Ellison, Doug Edmonds,
Comments: Accepted for publication in ApJ, 57 pages, 14 figures

From their abstract: "Due to the uncertainty in the location of the dust extinction, we arrive at two viable distances for the main ouflow component from the central source, 6 and 18 kpc, where we consider the 6 kpc location as somewhat more physically plausable. Assuming the canonical global covering of 20% for the outflow and a distance of 6 kpc, our analysis yields a mass flux of 120 M_sun yr^-1 and a kinetic luminosity that is ~0.1% of the bolometric luminosity of the object. Should the dust be part of the outflow, then these values are ~4x larger. The large mass flux and kinetic luminosity make this outflow a significant contributor to AGN feedback processes."

Neutral Gas Outflows and Inflows in Infrared-Faint Seyfert Galaxies
Hannah B. Krug, David S. N. Rupke, Sylvain Veilleux,
Comments: 50 pages, 12 figures, accepted for publication in ApJ

From their abstract: "The present paper describes the results from a search for outflows in 35 infrared-faint Seyferts with 10^9.9 < L_IR/L_sun < 10^11, or, equivalently, star formation rates (SFR) of ~0.4 -- 9 solar masses per year, to attempt to isolate the source of the outflow. We find that the outflow detection rates for the infrared-faint Seyfert 1s (6%) and Seyfert 2s (18%) are lower than previously reported for infrared-luminous Seyfert 1s (50%) and Seyfert 2s (45%). The outflow kinematics of infrared-faint and infrared-bright Seyfert 2 galaxies resemble those of starburst galaxies, while the outflow velocities in Seyfert 1 galaxies are significantly larger. Taken together, these results suggest that the AGN does not play a significant role in driving the outflows in most infrared-faint and infrared-bright systems, except the high-velocity outflows seen in Seyfert 1 galaxies."

Radiation-Driven Outflows in Active Galactic Nuclei
Daniel Proga, Ryuichi Kurosawa,
Comments: 9 pages, 5 figures, in Recent Directions In Astrophysical Quantitative Spectroscopy And Radiation Hydrodynamics: Proceedings of the International Conference in Honor of Dimitri Mihalas for His Lifetime Scientific Contributions on the Occasion of His 70th Birthday (AIP Conference Proceedings 1171)

Interstellar Medium / Hydrodynamics

Flows along cometary tails in the Helix planetary nebula NGC 7293
John Meaburn, Panos Boumis,
Comments: 8 pages, 4 figures, accepted for publication in MNRAS

Properties of extra-planar HI clouds in the outer part of the Milky Way
L. Dedes, P.W.M Kalberla,
Comments: 9 pages, 5 figures, 3 tables, Accepted for publication in A&A

Observations of 'wisps' in magnetohydrodynamic simulations of the Crab Nebula
N. F. Camus, S. S. Komissarov, N. Bucciantini and P. A. Hughes, 2009, MNRAS, 400, 1241
Full Text: HTML, PDF (Size: 7435K)

Turbulence and the formation of filaments, loops and shock fronts in NGC 1275 in the Perseus Galaxy Cluster
D. Falceta-Goncalves, E. M. de Gouveia Dal Pino, J. S. Gallagher, A. Lazarian,

X-ray Astronomy

Methods for Estimating Fluxes and Absorptions of Faint X-ray Sources
Konstantin V. Getman, Eric D. Feigelson, Patrick S. Broos, Leisa K. Townsley, Gordon P. Garmire,
Comments: Accepted for publication in The Astrophysical Journal. 39 pages, 15 figures

Stars, Supernovae and Planets

Introduction to nuclear astrophysics
Comments: Proceedings of the 5th European Summer School on Experimental Nuclear Astrophysics, Santa Tecla, Italy, 2009, 20 pages, 4 figures, 1 table

Molecular Clouds as a Probe of Cosmic-Ray Acceleration in a Supernova Remnant
Yutaka Fujita, Yutaka Ohira, Shuta J. Tanaka, Fumio Takahara,
Comments: Accepted for publication in ApJ Letters

Discovery of Multiple High-Velocity Narrow Circumstellar Na I D Lines in Nova V1280 Sco
Kozo Sadakane, Akito Tajitsu, Sahori Mizoguchi, Akira Arai, Hiroyuki Naito,
Comments: Accepted for PASJ letter, 5 pages, 8 figures

Retired A Stars and Their Companions. III. Comparing the Mass-Period Distributions of Planets Around A-Type Stars and Sun-Like Stars
Brendan P. Bowler, John Asher Johnson, Geoffrey W. Marcy, Gregory W. Henry, Kathryn M. G. Peek, Debra A. Fischer, Kelsey I. Clubb, Michael C. Liu, Sabine Reffert, Christian Schwab, Thomas B. Lowe,
Comments: Accepted by the Astrophysical Journal; 15 pages, 15 figures

From their abstract: "Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~ 50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets."

Other

A Multilingual on-line Dictionary of Astronomical Concepts
M. Heydari-Malayeri,

Comments: 3 pages, Interactive dictionary of Astronomy and Astrophysics, see: this http URL

## Wednesday, December 02, 2009

### BBC discusses costs of ESA Cosmic Vision contenders

An article on the BBC by Jonathan Amos discusses the contenders for the two slots in ESA's Cosmic Visions program for 2017-2018 launches. Interestingly the article's focus is on the costs (see graph taken from article), but it also has a nice description of each mission (many of which I hadn't heard of).

The missions, and my shorter summary of their nature and aims, are:

• SPICA: Joint ESA/JAXA infrared space telescope (5 to 210 micron wavelength range) with a 3.5m primary mirror.
• Euclid: Map mass distributions using baryonic acoustic oscillations and weak lensing.
• PLATO: A planet hunter with a particular emphasis on finding Earth-like and super-earth terrestrial planets using milli-magnitude accuracy photometry.
• Solar Orbiter: Study the Sun and Solar wind from a relatively close-in orbit (as close as 48 Solar radii, it claims).
• Marco Polo: Joint ESA/JAXA sample return mission from a near-earth asteroid. Note the high cost!
• Cross-Scale: Study MHD plasma properties in the terrestrial magnetosphere and bow shock. 7 ESA spacecraft forming 2 nested tetrahedra with a shard corner. (International collaboration will produce the optimum fleet of 12 spacecraft in 3 nested tetrahedra.) High cost!

## Friday, November 20, 2009

### Interesting Astrophysics: Nov 16 to 20

Its a quiet week in terms of interesting papers and preprints. Given the small number of papers no added introduction to them is necessary.

Galaxies and Starbursts

On the interstellar medium and star formation demographics of galaxies in the local universe
Matthew S. Bothwell, Robert C. Kennicutt Jr, and Janice C. Lee, 2090, MNRAS, 400, 154
Full Text: HTML, PDF (Size: 1632K)

Photodissociation chemistry footprints in the Starburst galaxy NGC 253
Sergio Martin, J. Martin-Pintado, S. Viti,
Comments: 32 pages, 4 figures, Published in ApJ
Journal-ref: 2009 ApJ 706 1323-1330

Origin(s) of the Highly Ionized High-Velocity Clouds Based on Their Distances
N. Lehner, J. C. Howk,
Comments: Submitted to the ApJ Letters

Black Holes and AGN

Quasar Outflow Contribution to AGN Feedback: Observations of QSO SDSS J0838+2955
Maxwell Moe, Nahum Arav, Manuel A. Bautista, Kirk T. Korista,
Comments: 28 pages, 7 figures, 4 tables, published in Astrophysical Journal
Journal-ref: 2009 ApJ 706 525-534

Their full abstract: "We present a detailed analysis of the Astrophysical Research Consortium 3.5 m telescope spectrum of QSO SDSS J0838+2955. The object shows three broad absorption line (BAL) systems at 22,000, 13,000, and 4900 km s^-1 blueshifted from the systemic redshift of z=2.043. Of particular interest is the lowest velocity system that displays absorption from low-ionization species such as Mg II, Al II, Si II, Si II*, Fe II and Fe II*. Accurate column densities were measured for all transitions in this lowest velocity BAL using an inhomogeneous absorber model. The ratio of column densities of Si II* and Fe II* with respect to their ground states gave an electron number density of log n_e (cm^-3) = 3.75 +/- 0.22 for the outflow. Photoionization modeling with careful regards to chemical abundances and the incident spectral energy distribution predicts an ionization parameter of log U_H = -1.93 +/- 0.21 and a hydrogen column density of log N_H (cm^-2) = 20.80 +/- 0.28. This places the outflow at 3.3+1.5-1.0 kpc from the central AGN. Assuming that the fraction of solid angle subtended by the outflow is 0.2, these values yield a kinetic luminosity of (4.5+3.1-1.8) x 10^45 erg s^-1, which is (1.4+1.1-0.6)% the bolometric luminosity of the QSO itself. Such large kinetic luminosity suggests that QSO outflows are a major contributor to AGN feedback mechanisms."

Numerical Astrophysics and Hydrodynamics

Turbulence modeling and the physics of the intra-cluster medium

L. Iapichino, A. Maier, W. Schmidt, J. C. Niemeyer,
Comments: To appear in the proceedings of the "Invisible Universe International Conference"

Characterizing Magnetohydrodynamic Turbulence in the Small Magellanic Cloud
Blakesley Burkhart, Snezana Stanimirovic, Alex Lazarian, Grzegorz Kowal,

Stars, Supernovae and Planets

A Feature Movie of SiO Emission 20-100 AU from the Massive Young Stellar Object Orion Source I
L. D. Matthews, L. J. Greenhill, C. Goddi, C. J. Chandler, E. M. L. Humphreys, M. Kunz,

Comments: Accepted to ApJ (January 2010); a full resolution version along with two accompanying GIF movies may be found at this http URL

An Unusually Fast-Evolving Supernova
Dovi Poznanski, Ryan Chornock, Peter E. Nugent, Joshua S. Bloom, Mohan Ganeshalingam, Douglas C. Leonard, Weidong Li, Rollin C. Thomas,
Comments: Science in press, first published online on Nov 5, 2009 in Science Express. Includes supporting online materia

The low-mass Initial Mass Function in the 30 Doradus starburst cluster
M. Andersen, H. Zinnecker, A. Moneti, M. J. McCaughrean, B. Brandl, W. Brandner, G. Meylan, D. Hunter,
Comments: Accepted in ApJ. Abstract abridged

How Common are Extrasolar, Late Heavy Bombardments?
Mark Booth, Mark C. Wyatt, Alessandro Morbidelli, Amaya Moro-Martín, Harold F. Levison,
Comments: 2 pages, 1 figure. Contribution to the conference proceedings for 'Pathways towards habitable planets'

Other

A Vigorous Explorer Program
Martin Elvis, et al, Comments: 18 pages, no figures. An Activities/Program White Paper submitted to the Astro2010 NAS/NRC Decadal Review of Astronomy and Astrophysics

## Friday, November 13, 2009

### Interesting Astrophysics: Nov 09 to 13

A mixed set of interesting preprints this week, with a strong emphasis on winds, either supernova-driven winds starbursts at high redshift (Kornei et al) or possibly from the center of our own galaxy (Law), and even outflows driven by black holes (King).

A second theme with a strong showing of interesting papers is astrobiology: the biological effects of radiation from "normal" stellar processes on the main sequence (Cuntz et al) or from Gamma ray bursts (Martin et al).

Galaxies and Starbursts

Morphologies of local Lyman break galaxy analogs II: A Comparison with galaxies at z=2-4 in ACS and WFC3 images of the Hubble Ultra Deep Field
R.A. Overzier, T.M. Heckman, D. Schiminovich, A. Basu-Zych, T. Goncalves, D.C. Martin, R.M. Rich,
Comments: Submitted to ApJ (14 pages, 7 figures). For a high-resolution colour version and background material, see this http URL

The Relationship Between Stellar Populations and Lyman Alpha Emission in Lyman Break Galaxies
Katherine A. Kornei, Alice E. Shapley, Dawn K. Erb, Charles C. Steidel, Naveen A. Reddy, Max Pettini, Milan Bogosavljevic,
Comments: 24 pages, 15 figures, submitted to ApJ

From their abstract: "We accordingly conclude that, within the LBG sample, objects with strong Lya emission represent a later stage of galaxy evolution in which supernovae-induced outflows have reduced the dust covering fraction. We also examined the hypothesis that the attenuation of Lya photons is lower than that of the continuum, as proposed by some, but found no evidence to support this picture."

A Multiwavelength View of a Mass Outflow from the Galactic Center
C. J. Law,
Comments: Accepted to ApJ. 15 pages, 8 (compressed) figures

From the abstract: "I compare the physical conditions of the GC lobe to several models and find best agreement with the canonical starburst outflow model. The formation of the GC lobe is consistent with the currently observed pressure and star formation rate in the central tens of parsecs of our Galaxy. Outflows of this scale are more typical of dwarf galaxies and would not be easily detected in nearby spiral galaxies. Thus, the existence of such an outflow in our own Galaxy may indicate that it is relatively common phenomenon in the nuclei of spiral galaxies."

Black Holes and AGN

Discovery of a 115 Day Orbital Period in the Ultraluminous X-ray Source NGC 5408 X-1
Tod E. Strohmayer,
Comments: Accepted for Publication in the Astrophysical Journal Letters

Black Hole Outflows
A.R. King,

Numerical Astrophyics

Generating on-the-fly large samples of theoretical spectra through N-dimensional grid
Ching-Wa Yip,
Comments: 7 pages, 5 figures, 1 table. Accepted for publication in AJ

Stars, Supernovae and Planets

Biological Damage due to Photospheric, Chromospheric and Flare Radiation in the Environments of Main-Sequence Stars
M. Cuntz, E. F. Guinan, R. L. Kurucz,
Comments: 8 pages, 4 figues, Planetary Systems as Potential Sites for Life, Invited Paper, IAU Symposium 264, eds. A. Kosovichev et al. (San Francisco: Astr. Soc. Pac.), in press

Effects of Gamma Ray Bursts in Earth Biosphere
Osmel Martin, Rolando Cardenas, Mayrene Guimaraes, Liuba Penate, Jorge Horvath, Douglas Galante,
Comments: Accepted for publication in Astrophysics &amp; Space Science

## Friday, November 06, 2009

### Interesting Astrophysics: Nov 02 to Nov 06

Of particular note this week are Crighton et al (who suggest a particular case of intergalactic metal line absorption can be associated with a z=0.2272 galaxy polluting a region ~200 kpc in radius), Bertone et al (metal line cooling from the IGM predicted in the OWLS simulations) Risaliti & Elvis (a line driven model for AGN winds), and Bond et al (terrestrial planet formation models that correctly predict the observed elemental abundances also predict that terrestrial planets form wet and do not need significant water delivery from comets).

Galaxies and Starbursts

Searching for Evidence of Energetic Feedback in Distant Galaxies: A Galaxy Wide Outflow in a z~2 Ultraluminous Infrared Galaxy
D.M. Alexander, A.M. Swinbank, I. Smail, R. McDermid, N. Nesvadba,
Comments: 10 pages, 5 figures, 1 table. Resubmitted to MNRAS after taking account of referees feedback

Galaxies at Redshift ~0.5 Around Three Closely Spaced Quasar Sightlines
Neil H. M. Crighton, Simon L. Morris, Jill Bechtold, Robert A. Crain, Buell T. Jannuzi, Allen Shone, Tom Theuns,
Comments: 45 pages, 21 figures. Accepted by MNRAS

From their abstract: "We identify a galaxy at z=0.2272 with associated metal absorption in two sightlines, each 200 kpc away. By constraining the star formation history of the galaxy, we show the gas causing this metal absorption may have been enriched and ejected by the galaxy during a burst of star formation 2 Gyr ago."

Enhanced Dense Gas Fraction in Ultra-Luminous Infrared Galaxies
S. Juneau, D. T. Narayanan, J. Moustakas, Y. L. Shirley, R. S. Bussmann, R. C. Kennicutt Jr, P. A. Vanden Bout,
Comments: 20 pages, 10 figures. To be published in The Astrophysical Journal (accepted)

Black Holes and AGN

Comparison between the Luminosity functions of X-ray and [OIII] selected AGN
I. Georgantopoulos, A. Akylas,
Comments: 7 pages to appear in Astronomy & Astrophysics

A non-hydrodynamical model for acceleration of line-driven winds in Active Galactic Nuclei
G. Risaliti, M. Elvis,
Comments: 15 pages, 9 figures. Accepted for publication in Astronomy &amp; Astrophysics

Numerical Astrophysics

Metal-line emission from the warm-hot intergalactic medium: I. Soft X-rays
Serena Bertone, Joop Schaye, Claudio Dalla Vecchia, C.M. Booth, Tom Theuns, Robert P.C. Wiersma, The Enrichment of Intergalactic Medium With Adiabatic Feedback I: Metal Cooling and Metal Diffusion
Sijing Shen, James Wadsley, Gregory Stinson,
Comments: 16 pages, 11 figures, submitted to MNRAS

Ram-pressure stripping of halo gas in disc galaxies: implications for galactic star formation in different environments
Kenji Bekki, 2009, MNRAS, 399, 2221
Full Text: HTML, PDF (Size: 4409K)

The impact of feedback on the low redshift Intergalactic Medium
Luca Tornatore, Stefano Borgani, Matteo Viel, Volker Springel,

Stars, Supernovae and Planets

Making the Earth: Combining Dynamics and Chemistry in the Solar System
Jade C. Bond, Dante S. Lauretta, David P. O'Brien,
Comments: 61 pages (including online material), 12 figures (7 in paper, 5 online). Accepted to Icarus

From their abstract: "Bulk elemental abundances based on disk equilibrium studies have been determined for the simulated terrestrial planets of O'Brien et al. (2006). These abundances are in excellent agreement with observed planetary values, indicating that the models of O'Brien et al. (2006) are successfully producing planets comparable to those of the Solar System in terms of both their dynamical and chemical properties. Significant amounts of water are accreted in the present simulations, implying that the terrestrial planets form "wet" and do not need significant water delivery from other sources. Under the assumption of equilibrium controlled chemistry, the biogenic species N and C still need to be delivered to the Earth as they are not accreted in significant proportions during the formation process."

## Friday, October 30, 2009

### Interesting Astrophysics: 26 Oct to 30 Oct

Galaxies and Starbursts

A New Empirical Method to Infer the Starburst History of the Universe from Local Galaxy Properties
Philip F. Hopkins, Lars Hernquist,
Comments: 21 pages, 8 figures, accepted to MNRAS

Constraining the initial mass function of stars in the Galactic Centre
Ulf Loeckmann, Holger Baumgardt, Pavel Kroupa,
Comments: MNRAS, accepted, 8 pages, 4 figures

HI Selected Galaxies in the Sloan Digital Sky Survey I: Optical Data
Andrew A. West, Diego A. Garcia-Appadoo, Julianne J. Dalcanton, Mike J. Disney, Constance M. Rockosi, Zeljko Ivezic, Misty C. Bentz, J. Brinkmann,
Comments: 14 pages, 8 Figures, accepted for publication in AJ. Complete tables will be available in the AJ electronic version and on the Vizier site

HI Selected Galaxies in the Sloan Digital Sky Survey II: The Colors of Gas-Rich Galaxies
Andrew A. West, Diego A. Garcia-Appadoo, Julianne J. Dalcanton, Mike J. Disney, Constance R. Rockosi, Zeljko Ivezic,
Comments: 12 pages, 16 figures, published in AJ (138, 796); replaced Figure 16 with higher resolution version
Journal-ref: West et al. 2009, AJ, 138, 796

Numerical Astrophysics

Adaptive Mesh Fluid Simulations on GPU
Peng Wang, Tom Abel, Ralf Kaehler,

CUDA & MPI, with what sounds like the ZEUS MHD scheme. Hardly surprising, but nice to see some effort going into exploring the use of GPU computing with hydro codes.

Stars, Supernovae and Planets

Evolution of supermassive stars as a pathway to black hole formation
Mitchell C. Begelman,
Comments: 10 pages, 5 figures, to appear in Monthly Notices of the Royal Astronomical Society

X-ray observations of classical novae. Theoretical implications
M. Hernanz, G. Sala,
Comments: 6 pages, review paper accepted for publication in Astronomische Nachrichten

The Nature and Nurture of Star Clusters
Bruce G. Elmegreen,
Comments: to be published in IAUS266: Star Clusters Basic Galactic Building Blocks Throughout Time And Space, eds. Richard de Grijs and Jacques Lepine, Cambridge University Press, 11 pages

Nuclear Star Clusters
Torsten Boeker,
Comments: invited talk at IAU Symp. 266 "Star Clusters: Galactic Building Blocks through Space and Time"

## Friday, October 23, 2009

### Interesting Astrophysics: Oct 12 to Oct 23

This edition of Interesting Astrophysics spans an even wide range of topics than normal, from C IV in the IGM (D'Odorico et al), X-ray emission from galaxies (Laird et al, Pietsch), a variety of supernova-related preprints, to AGN feedback/outflows and other topics I've not mentioned.

Galaxies and Starbursts

An Anisotropic Propagation Model for Galactic Cosmic Rays
Iris Gebauer, Wim de Boer,
Comments: 19 pages, 19 figures, submitted to A&amp;A

The rise of the C IV mass density at z<2.5
Valentina D'Odorico, Francesco Calura, Stefano Cristiani, Matteo Viel,
Comments: Paper accepted by MNRAS. The parameters of the C IV line fitting will be available in electronic format

The radial distribution of core-collapse supernovae in spiral host galaxies
A. A. Hakobyan, G. A. Mamon, A. R. Petrosian, D. Kunth, M. Turatto,
Comments: 10 pages, 6 figures, 5 tables. Astronomy &amp; Astrophysics, in press

On the X-ray properties of submm-selected galaxies
Elise S. Laird, Kirpal Nandra, Alexandra Pope, Douglas Scott,
Comments: 12 pages, 5 figures, accepted for publication in MNRAS

X-ray emission from optical novae in M 31
W. Pietsch,
Comments: 6 pages, 4 figures, accepted for publication in Aston.Nachr

Bars in Starbursts and AGNs -- A Quantitative Reexamination
Lei Hao, Shardha Jogee, Fabio D. Barazza, Irina Marinova, Juntai Shen,
Comments: 8 pages, 3 figures, to be published in "Galaxy Evolution: Emerging Insights and Future Challenges", ed. S. Jogee et al., Astron. Soc. Pacific, 2009

From their abstract: "We find that AGN and star-forming galaxies have similar optical bar fractions, 47% and 50%, respectively. Both bar fractions are higher than that in inactive galaxies (29%)."

Extragalactic CS survey
Comments: 17 pages, 16 figures, 3 tables, Accepted to ApJ

From the abstract: "We present a coherent and homogeneous multi-line study of the CS molecule in nearby (D$<$10Mpc) galaxies. We include, from the literature, all the available observations from the $J=1-0$ to the $J=7-6$ transitions towards NGC 253, NGC 1068, IC 342, Henize~2-10, M~82, the Antennae Galaxies and M~83."

Black Holes and AGN

Feeding and Feedback in nearby AGN from Integral Field Spectroscopy
Thaisa Storchi-Bergmann,
Comments: 4 pages, 2 figures, to appear in the proceedings of the conference "The Monster's Fiery Breath", eds. Sebastian Heinz and Eric Wilcots

From the abstract: "The ionized gas, on the other hand, traces the AGN feedback. Its
kinematics shows two components: (1) one originating in the plane, and
dominated by circular rotation; (2) another outflowing along the Narrow-Line
Region (NLR) whose flux distribution and kinematics frequently correlate with
structures seen in radio maps. Mass outflow rates along the NLR range from
10^-2 to 1 M_sun yr^-1, corresponding to 10-100 times the accretion rate to the
AGN, indicating that most of the NLR gas mass has been entrained from the
galaxy plane. The average kinetic power of the NLR outflows is ~10^-4 times the
bolometric luminosity.
"

AGN Feedback: Does it work?
Smita Mathur, Rebecca Stoll, Yair Krongold, Fabrizio Nicastro, Nancy Brickhouse, Martin Elvis,
Comments: to appear in proceedings of the conference "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June 2009, Madison, WI, Eds. S. Heinz &amp; E. Wilcots

Interstellar Medium

PAH processing in interstellar shocks
E. R. Micelotta, A. P. Jones, A. G. G. M. Tielens,
Comments: 21 pages, 11 figures, accepted for publication in Astronomy and Astrophysics

VLT/FLAMES-ARGUS observations of stellar wind--ISM cloud interactions in NGC 6357
M.S. Westmoquette, J.D. Slavin, L.J. Smith, J.S. Gallagher III,
Comments: 9 pages, 5 figures (3 colour). Accepted for publication in MNRAS

Stars, Supernovae and Planets

The rebrightening of planetary nebulae through ISM interaction

C J Wareing,

Comments: Review paper accepted to PASA. 8 pages, 5 figures. High resolution images available from the author

Stellar Feedback in Molecular Clouds and its Influence on the Mass Function of Young Star Clusters
S. Michael Fall, Mark R. Krumholz, Christopher D. Matzner,
Comments: 5 pages, 2 figures, emulateapj format, submitted to ApJL

Typing Supernova Remnants Using X-ray Line Emission Morphologies
Laura A. Lopez, Enrico Ramirez-Ruiz, Carles Badenes, Daniela Huppenkothen, Tesla E. Jeltema, David A. Pooley,
Comments: 4 pages, 1 figure, accepted for publication in ApJL

Line-of-sight Shell Structure of the Cygnus Loop
Hiroyuki Uchida, Hiroshi Tsunemi, Satoru Katsuda, Masashi Kimura, Hiroko Kosugi, Hiroaki Takahashi,
Comments: 8 pages, 7 figures, accepted for publication in ApJ
Journal-ref: Astrophysical Journal 705 (2009) 1152-1159

Other

FISH: A 3D parallel MHD code for astrophysical applications
R. Kaeppeli, S. C. Whitehouse, S. Scheidegger, U.-L. Pen, M. Liebendoerfer,

Astrometry.net: Blind astrometric calibration of arbitrary astronomical images
Dustin Lang, David W. Hogg, Keir Mierle, Michael Blanton, Sam Roweis,

A very cool idea!

## Friday, October 09, 2009

### Interesting Astrophysics: 05 Oct to 09 Oct

A mixed bag of interesting preprints this week. Of note are local analogs of the Lyman Break Galaxies (Overzier et al), the radio-FIR correlation at high z (Lacki & Thompson), and a possible optical counterpart to an intermediate mass black hole candidate (Soria et al).

Galaxies and Starbursts

Local Lyman Break Galaxy Analogs: The Impact of Massive Star-forming Clumps on the Interstellar Medium and the Global Structure of Young, Forming Galaxies
R.A. Overzier, T.M. Heckman, C. Tremonti, L. Armus, A. Basu-Zych, T. Goncalves, R.M. Rich, D.C. Martin, A. Ptak, D. Schiminovich, H.C. Ford, B. Madore, M. Seibert,
Comments: The Astrophysical Journal, In Press (22 pages, 16 figures). For the full version with high-resolution colour figures, see: this http URL

Stationary models for the extra-planar gas in disc galaxies
F. Marinacci, F. Fraternali, L. Ciotti, C. Nipoti,
Comments: 14 pages, 7 figures, accepted for pubblication in MNRAS

A cloudy halo model.

The Physics of the FIR-Radio Correlation: II. Synchrotron Emission as a Star-Formation Tracer in High-Redshift Galaxies
Brian C. Lacki, Todd A. Thompson,

The fundamental gas depletion and stellar-mass buildup times of star forming galaxies
Jan Pflamm-Altenburg, Pavel Kroupa,
Comments: accepted for publication in ApJ

The WMAP haze from the Galactic Center region due to massive star explosions and a reduced cosmic ray scale height
Peter L. Biermann, Julia K. Becker, Gabriel Caceres, Athina Meli, Eun-Suk Seo, Todor Stanev,

Black Holes and AGN

The Activity of the Neighbours of AGN and Starburst Galaxies: Towards an evolutionary sequence of AGN activity
E.Koulouridis, M.Plionis, V.Chavushyan, D.Dultzin, Y.Krongold, I.Georgantopoulos, C.Goudis,
Comments: 50 pages, 5 figures, 41 spectra

Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
Roberto Soria, George K. T. Hau, Alister W. Graham, Albert K. H. Kong, N. Paul M. Kuin, I-Hui Li, Ji-Feng Liu, Kinwah Wu,
Comments: 5 pages, submitted to MNRAS Letters. Contact R Soria for higher-resolution figures

Theoretical and Numerical Astrophysics, including Cosmology

Pressure Support vs. Thermal Broadening in the Lyman-alpha Forest II: Effects of the Equation of State on Transverse Structure
Molly S. Peeples, David H. Weinberg, Romeel Davé, Mark A. Fardal, Neal Katz,
Comments: 11 figures, submitted to MNRAS

Stars, Supernovae and Planets

Ionized Gas Towards Molecular Clumps: Physical Properties of Massive Star Forming Regions
Katharine G. Johnston, Debra S. Shepherd, James E. Aguirre, Miranda K. Dunham, Erik Rosolowsky, Kenneth Wood,
Comments: 67 pages, 16 figures, 8 tables, accepted for publication in ApJ

From their abstract: "For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7 +/- 8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars."

## Thursday, October 08, 2009

### HuffPo lunacy

The Huffington Post has a certain reputation for allowing (perhaps it would be more accurate to say promoting) quacks, vaccine denialists, conspiracy theorists and other superstitious wackery, but the example that follows is impressively moronic even by HuffPo standards.

As Tariq Malik at Space.com reports regarding NASA's LCROSS lunar impact (emphasis mine):

NASA's LCROSS mission will slam a spacecraft and an empty rocket stage into the moon's south pole Friday morning at 7:31 a.m. EDT (1131 GMT) in a search for water ice buried in the perpetual shadows of lunar craters.

Scientists are eagerly awaiting the LCROSS crashes and hope they'll provide a definitive answer on whether lunar water ice could be used to support future astronauts on the moon. But at least one person — novelist and screenwriter Amy Ephron — has spoken out against the \$79 million mission on her Huffington Post blog and launched a Twitter campaign ("helpsavethemoon") to save the moon from future onslaught.

"I'm not a big fan of explosions, anyway. In Iraq or Afghanistan or the South Pole of the Moon. But who does have a territorial prerogative there?" Ephron wrote. "Who has jurisdiction? Who has the right to say that it's okay to blow up a crater on the moon?"

Apparently, Mother Nature does. The moon is covered in craters, with new ones like those to be created by the LCROSS probes popping up all the time by meteorites that pummel the lunar surface.

"The image of this impact, what we're doing with the moon, is something that occurs naturally four times a month on the moon, whether we're there or not," LCROSS principal investigator Tony Colaprete told reporters Thursday.

I love Malik and Colaprete's understated but effectively utter refutation of Ephron's deliberately ignorant rant. Keep it up!

### New mega ring around Saturn discovered using Spitzer

Infrared observations using the Spitzer Space Telescope, published by Verbiscer et al (2009, Nature), have revealed the largest known ring around Saturn, an annulus of very tenuous material extending between 6 million and 18 million kilometers from Saturn, and tilted by 27 degree from the plane of the traditional rings (which only extend out to ~240,000 km).

The material in the new ring comes from the battered and cratered moon Phoebe. Of more interest, this new dust ring explains why the leading side of Iapetus is so much darker than the rest of it - the dark front surface of Iapetus is material from the ring swept up by Iapetus as it orbits at the inner edge of the new ring.

In truth a link between the dark front of Iapetus and Phoebe has been suspected before now, as the composition of the dark material is very similar to that of Phoebe based on near IR spectroscopy with Cassini. What the Spitzer observations reveal is the presence of the dust ring and hence the mechanism of material transfer from Phoebe to Iapetus.

Although the ring is physically huge, with a volume of ~5e21 km^3 (this is my BOTE calculation. As far as I can tell Verbiscer et al do not quote a volume), it is incredibly tenuous, and if all the material within it were collected back into one place it would possibly only occupy ~ 1 km^3 of rock, i.e. the volume of a crater on Phoebe.

The other interesting thing is that the material migrates inwards under the influence of radiation pressure. From Verbiscer et al:

On long timescales, collisions and inward transport become important. Collision with Phoebe, the dominant loss mechanism for particles larger than several centimetres in size, takes on the order of 1010 years. Re-radiation of absorbed sunlight exerts an asymmetric force on dust grains, causing them to spiral in towards Saturn with a characteristic timescale of 1.5 105rg years where rg is the particle radius in micrometres. This force brings all centimetre-sized and smaller material to Iapetus and Titan unless mutual particle collisions occur first. The rate of mutual collisions depends on the size distribution of the ring particles and optical depth; if the ring were comprised entirely of 10 m grains, then the collisional timescale would be tens of millions of years, which is comparable to the inward drag timescale. Most material from 10 m to centimetres in size ultimately hits Iapetus, with smaller percentages striking Hyperion and Titan3.

References:

Verbiscer, A., Skrutskie, M., & Hamilton, D. (2009). Saturn's largest ring Nature DOI: 10.1038/nature08515

BBC article published by Jonathan Amos. 2009/10/08 (the source of the nice graphic shown above).

Spitzer press release, 2009/10/06.