Thursday, August 22, 2019

Mauna Kea

Looking toward the summit of Mauna Kea, from the small hill near the base of the access road. Taken in 2005.

A view from the summit, looking toward the Keck telescopes. Taken in 2005.

Saturday, July 07, 2018

Colorful binary star systems for small telescopes: Part 2

I previously discussed my ongoing attempt to develop an automated method of getting the physical properties of binary/multiple star systems visible to amateur astronomers. In Part 1 I got as far as getting basic observables and IDs for the Primary stars in Bob King's article,"Colored Double Stars, Real and Imagined" by Bob King (Sky & Telescope, December 14 2016).

The next step, described here, is to use the the Washington Double Star Catalog to identify and list the probably companions of each Primary. The WDS is an ongoing project that summarizes observations of bright visual double or multiple stars. Their aim is to determine which, if any, are physically associated in a gravitationally bound stellar systems as opposed to being chance line of sight superpositions. As such the WDS project makes use of multiple historical observations, measured distances (by parallax) and proper motions, the results of which are summarized in their catalog.

To cut a long story short I've written some bash and python scripts that download the latest WDS catalog from Vizier, then takes the outputs from the scripts described in Part 1 and combines that with the WDS catalog to come up with a list of Primary, Secondary, (Tertiary etc) stellar IDs based on some WDS-related selection criteria.

I was surprised to find that even for many visually bright double stars their exact status, as genuine binary or multiple star systems or as chance line-of-sight superpositions, is not currently 100% known. In addition, for some "classic" doubles, the latest information suggests they are likely not genuine binaries.

To illustrate this I'll continue to show examples based on Bob King's Colored Double Stars.

Firstly, we'll select components where the WDS catalog notes that there is evidence consistent with them being members of the same physical stellar system.

Then for purposes of comparison we'll separately select all WDS possible components but exclude those where there is evidence is against them being associated.

Filtering based on positive evidence for multiplicity

Here we are looking for double/multiple stellar systems where the available WDS info suggests they're real gravitationally bounds systems. To do this we select components with already determined actual orbits, or statistically similar parallax and/or proper motions (i.e. they're at close to the same distance and/or are moving in the sky in the same way). These correspond to the WDS 'Note' column entries 'C', 'O', 'T', 'V' or 'Z'.

python3 process_wds_ids.py king_processed.fits.gz king_wds_postv_ids.html \
  --wds-detail=king_wds_postv_detail.html --filter=positive
[...output trimmed for blog...]
0 input targets with no WDS info: []
8 input targets where positive filtering removed all components: ['1 Ari', 
   'iota Tri = 6 Tri', 'eta Per', '32 Eri', 'rho Ori', 'iota Ori', 'gamma Lep', 
   '24 Com']

This produced an HTML table of input star name and output component WDS IDs (king_wds_postv_ids.html), along with an optional separate table listing select information from the WDS catalog for each selected component (king_wds_postv_detail.html) which is shown below:
WDS Comp Obs2 pa2 sep2 mag1 mag2 SpType Notes
00491+5749 AB 2016 325 13.4 3.52 7.36 G1V+M NO P
02039+4220 BC 2010 96 0.2 5.3 6.5 B8V+A0V NO
05154+3241 Ca,Cb 1999 100 2.0 7.33 14.1 F2V+DA1.3 NV
07166-2319 BC 1999 165 999.9 5.84 6.76 A5m+F0 NV
08467+2846 2016 308 31.3 4.13 5.99 G7.5IIIa NV
14514+1906 AB 2017 300 5.6 4.76 6.95 G8V+K5V NO
17146+1423 AB 2017 104 4.8 3.48 5.4 M5Ib-II NO
18015+2136 2017 256 6.5 4.85 5.2 A5IIIn NV
18448+3736 AD 2017 150 43.8 4.34 5.62 F0IVv NZ V
19307+2758 AB 2017 54 34.6 3.19 4.68 K3II+B9.5 NZ
19307+2758 Aa,Ac 2008 101 0.4 3.37 5.16 K3III+B0V NO
20136+4644 Aa,Ab 1985 111 0.0 3.93 0.0 K4Ib+B3V NO
20210-1447 AB 2012 267 205.4 3.15 6.08 F8V+A0 NV
20210-1447 Aa,Ab 2014 42 0.0 3.1 4.9 F8V+A0 NO
20210-1447 Ba,Bb 2015 59 0.5 6.16 9.14 A0III NO
20467+1607 AB 2017 266 8.9 4.36 5.03 K1IV+F7V NO Z
22292+5825 AC 2017 192 40.7 4.21 6.11 F5Iab+B7 NZ

In addition to the 8 cases where the script noted there were no doubles with information that made them 'likely' physical companions, a look at the king_wds_postv_detail.html table shows some of the remaining objects aren't great visual doubles systems either.
  • gamma And: For WDS 02039+4220, the likely double is components B & C, i.e. not including gamma And itself! The two B & C components are only separated by 0.2 arcseconds. As we don't all have the Hubble Space Telescope this is effectively a spectroscopic binary system and not useful visual double.
  • 145 CMa: The same problem arises for J07166-2319 (called h3945 CMa in Bob King's list), where again the likely system is components B & C, not including the bright "primary" itself.
  • 14 Aur: For WDS 05154+3241 the only likely physical system is a spectroscopic binary system of component C. So once again the "primary" is not part of a likely physical binary systsem with any of its visually close neighbors. The second component of the Ca,Cb pair is a white dwarf, which is interesting, but at 14th magnitude is far too faint to see with a small amateur scope.
  • 31 Cyg: A similar situation arises for WDS 20136+4644, where in this case it is only the primary itself that survives filtering because it too is a spectroscopic binary.
The final thing to note is the systems where the likely companion to the primary is not the closest companion: zeta Lyr A & D and delta Cep A & C.

Filtering based on negative evidence for multiplicity

In this case we accept all WDS components except those where the evidence suggests they're not related, i.e. not part of the same physical system. The script remove components with statistically different parallax and/or proper motions, or are otherwise noted in the WDS as being of dubious validity. These correspond to the WDS 'Note' column entries 'S', 'U', 'X', and 'Y'.

python3 process_wds_ids.py king_processed.fits.gz king_wds_negtv_ids.html \
    --wds-detail=king_wds_negtv_detail.html --filter=negative
Processing 22 targets from king_processed.fits.gz
[...output trimmed for blog...]
0 input targets with no WDS info: []
0 input targets where negative filtering removed all components: []

This results in information overload, as too many candidate components that currently lack sufficient information to be rejected end up passing through the filter.
WDS Comp Obs2 pa2 sep2 mag1 mag2 SpType Notes
00491+5749 AB 2016 325 13.4 3.52 7.36 G1V+M NO P
00491+5749 BD 2000 1 172.2 7.36 12.8 K7V N P
01501+2217 2016 165 2.9 6.33 7.21 G3III N
02039+4220 A,BC 2016 63 9.4 2.31 5.02 K3IIb N
02039+4220 BC 2010 96 0.2 5.3 6.5 B8V+A0V NO
02124+3018 2016 69 3.7 5.26 6.67 G0III N
02507+5554 AB 2012 295 31.4 3.76 8.5 M3Ib-IIa N
02507+5554 AE 2012 297 242.9 3.76 9.24 M3Ib-IIa N
02507+5554 CD 2012 116 5.1 11.61 12.7 OB- N
02507+5554 CG 2012 230 15.3 11.61 14.0 OB- N
03543-0257 AB 2017 349 6.9 4.8 5.89 G8III+A2V N
03543-0257 AC 2003 5 165.9 4.8 10.5 G8III N
05133+0252 AB 2015 62 6.9 4.62 8.5 K2II N
05154+3241 AD 2010 322 179.7 5.03 10.75 A9IV N
05154+3241 BC 2014 210 22.7 10.9 7.33 +F2V N
05354-0555 AB 2012 141 11.6 2.77 7.73 O9III N
05354-0555 BC 2014 94 40.3 7.73 9.81 B4 N
05445-2227 AB 2012 350 95.0 3.64 6.28 F6V+K2V N
05445-2227 BC 1999 8 112.1 6.28 11.37 K2V NL
07166-2319 BC 1999 165 999.9 5.84 6.76 A5m+F0 NV
08467+2846 2016 308 31.3 4.13 5.99 G7.5IIIa NV
12351+1823 2016 272 20.4 5.11 6.33 K2III N
14514+1906 AB 2017 300 5.6 4.76 6.95 G8V+K5V NO
17146+1423 AB 2017 104 4.8 3.48 5.4 M5Ib-II NO
18015+2136 2017 256 6.5 4.85 5.2 A5IIIn NV
18448+3736 AD 2017 150 43.8 4.34 5.62 F0IVv NZ V
19307+2758 AB 2017 54 34.6 3.19 4.68 K3II+B9.5 NZ
20136+4644 AC 2016 173 108.6 3.93 6.97 K2II N
20136+4644 AD 2016 322 336.7 3.93 4.83 K2II N
20136+4644 CH 2014 62 60.6 6.97 12.6 B5V N
20136+4644 CI 2015 136 60.2 6.97 12.26 B5V N
20136+4644 DC 2003 150 431.8 4.83 6.97 A5IIIn N
20136+4644 FJ 2015 217 4.2 13.9 15.1 N R
20136+4644 HK 2015 262 8.9 11.74 10.87 N K
20210-1447 AB 2012 267 205.4 3.15 6.08 F8V+A0 NV
20210-1447 AC 2012 133 226.1 3.15 8.83 F8V+A0 N
20210-1447 BC 2000 111 396.7 6.08 8.83 A0III N
20210-1447 DE 2000 321 3.9 13.7 14.4 N
20467+1607 AB 2017 266 8.9 4.36 5.03 K1IV+F7V NO Z
22292+5825 AC 2017 192 40.7 4.21 6.11 F5Iab+B7 NZ
22292+5825 DE 2008 23 1.4 13.9 14.0 N

I've included the table for completeness, although I can't recommend using this form of filtering. A lot of faint components with large angular separations are listed, which simply aren't interesting from an amateur astronomical point-of-view.

What next?

This post is already very long and much delayed, so I'll put off the next stage of the process until Part 3. In that post we'll take our improved list of stars that includes the primary and likely companion IDs ("king_wds_postv_ids.html" above) and run that through the script from Part 1 that queries Simbad to get the observable properties: positions, magnitudes, parallaxes, proper motions, effective temperatures and spectral types for the stars. Once we have the observables we'll finally be ready to calculate the derived properties we're interested in: distance, luminosity, radius, and rough stellar masses.

Acknowledgements:

This research has made use of the Washington Double Star Catalog maintained at the U.S. Naval Observatory.

Wednesday, March 21, 2018

Colorful binary star systems for small telescopes: Part 1

I recently got a small telescope (a Celestron NexStar 6SE) in order to introduce the kids to the wonders of the sky, albeit somewhat dulled by suburban light pollution.

While waiting for the weather to become warm enough to actually use it I've been pondering what interesting objects can actually be seen given the constraints of the hardware. Randomly looking at things without knowing what they are can only get you so far, especially with kids.

One class of (non-Solar-system) object that can be visually impressive are visual double stars with a significant difference in color. Differences in color are easy for kids to understand as differences in temperature, which leads on to understanding there are different types of stars...

That thought lead me to this nice article,"Colored Double Stars, Real and Imagined" by Bob King, Sky & Telescope, December 14 2016. Its a good article, with images, information and even an HTML table of the objects, rough coordinates, magnitude and spectral types. I've reproduced the table below:

Star R.A. Dec. Mag A Mag B Sep. P.A. Color difference Spec. Class
η Cas 00h 49m +57° 49' 3.5 7.2 13" 317° 1.7 G0, K7
1 Ari 01h 50m +22° 16' 5.9 7.2 2.9" 164° 3.5 K1, A6
γ And 02h 04m +42° 20' 2.1 4.8 9.8" 64° 3.5 K3, B8
ι Tri = 6 Tri 02h 12m +30° 18' 5.3 6.7 4" 69° 1.0 G5, F5
η Per 02h 51m +55° 54' 3.8 8.5 28" 301° 3.0 K3, A3
32 Eri 03h 54m –02° 57' 4.8 5.9 7" 254° 2.6 G8, A2
ρ Ori 05h 13m +02° 52' 4.6 8.5 7" 64° 1.7 K3, F7
14 Aur 05h 15m +32° 41' 5.0 7.4 15" 226° 0.4 A9, F3
ι Ori 05h 35m +05° 57' 2.9 7.0 10.9" 142° 0.2 O9, B1
γ Lep 05h 44m –22° 27' 3.6 6.3 97" 350° 1.6 F6, K2
h3945 CMa 07h 17m –23° 19' 5.0 5.8 26.8" 52° 2.0 K0, F0
ι Cnc 08h 47m +28° 46' 4.0 6.6 30.6" 307° 2.6 G8, A2
24 Com 12h 35m +18° 23' 5.1 6.3 20" 270° 2.2 K0, A9
ξ Boo 14h 51m +19° 06' 4.8 7.0 6" 343° 0.5 G8, K4
α Her 17h 15m +14° 23' 3.1 5.4 5" 106° 1.7 M5, G8
95 Her 18h 02m +21° 36' 4.9 5.2 6" 258° 2.3 A5, G8
ζ Lyr 18h 45m +37° 36' 4.3 5.6 44" 150° 1.1 B7, A8
Albireo 19h 31m +27° 57' 3.4 4.7 35" 54° 3.5 K3, B8
31 Cyg 20h 14m +46° 44' 3.8 4.8 107" 325° 2.9 K2, B3
β Cap 20h 21m –14° 47' 3.2 6.1 207" 267° 3.2 K0, B8
γ Del 20h 47m +16° 07' 4.4 5.0 9" 267° 1.4 K1, F7
δ Cep 22h 29m +58° 25' 4.1 6.3 40.9" 191° 2.5 G2, B7

But it and the article still leave me with many questions I'd like to know answers for *before* actually trying to observe these systems and show them to my kids:
  • How far away are these stars?
  • What type of star are they? (main sequence dwarfs? Giants?)
  • What is their true luminosity, mass, radius, and temperature compared to the Sun?
  • How long do stars like these live?
  • How far apart physically are these stars?
  • Are they actually a binary (or multiple) star systems, or just chance alignments?
In addition to these questions, there are some issues with the list as presented that make it hard to use it.
  • What are the names/identifiers of the companion stars? The names given above are presumably the Primary, i.e. visually brightest, member of the pair. But what are the other member or members of the system?
  • What are the true coordinates of the objects? The RA/Decs given above are rounded to the nearest minute and arc-minute. One minute in RA is 15 arcminutes, or half the angular diameter of the moon. The number of objects in a professional astronomical catalog within a 15 arcminute radius is likely pretty large.
  • The Celestron recognizes SAO star identifiers, so what are those for the objects given above?
As I used to be a professional astronomer I know answers to all these questions either already exist, or can be determined to some level of accuracy for such bright (and hence nearby) stars and accessed via SIMBAD (wikipedia entry here). Its just a matter of collating the right information from different astronomers and applying some scientific criteria to choose between multiple, quite possibly contradictory, sources of information. I started trying to collate that information, but after spending quite some time getting only the basic beginnings of what I needed I discovered I'd somehow missed a bunch of the stars listed in Bob King's table and hence wasn't even close to being finished.  Argh!

There had to be a better, more automated, way of getting the information. So I set out to write one, of which the DoubleStars github project is the first installment. The table shown below is one of the outputs of star_query.py after processing the HTML table from Bob King's article (above), more information than shown is written to an additional gzipped fits-format table.

For each input target the table below shows the official SIMBAD identifier, along with additional identifiers recognized by Simbad. In particular the Washington Double Star ID (to investigate the true status of the visual double as a binary system), the SAO ID (for controlling the NexStar), and the Hipparcos Output Catalog (HIP, for parallax and hence true distance). The Henry Draper (HD) ID is useful when searching in Kstars (which can also be used to control the NexStar). In addition, more accurate RA and Dec, spectral types with luminosity class, and in some cases stellar effective temperature (in Kelvin) and metal abundance are given (presumably again for the Primary).

Star SimbadID WDS SAO HIP NAME HD RA_icrs DEC_icrs magV spec_type Teff_(Fe_H) [Fe/H]
eta Cas * eta Cas J00491+5749AB 21732 3821 Achird 4614 0:49:06.3 57:48:54.7 3.44 F9V+M0-V 5899 -0.31
1 Ari * 1 Ari J01501+2217AB 74966 8544 None None 1:50:08.6 22:16:31.2 5.86 G3III+A3IV 0 0.00
gamma And * gam And J02039+4220A,BC None 9640 Almach None 2:03:54.0 42:19:47.0 2.10 K3II+B9.5V+A0V 0 0.00
iota Tri = 6 Tri * iot Tri J02124+3018AB 55347 10280 None 13480 2:12:22.3 30:18:11.0 4.95 G0III+G5III 0 0.00
eta Per * eta Per J02507+5554A 23655 13268 Miram 17506 2:50:41.8 55:53:43.8 3.79 K3-Ib-IIa 3500 0.09
32 Eri * 32 Eri J03543-0257AB None 18255 None None 3:54:17.5 -2:57:17.0 4.45 G8III+A1V 0 0.00
rho Ori * rho Ori J05133+0252AB 112528 24331 None 33856 5:13:17.5 2:51:40.5 4.44 K1III 4599 0.22
14 Aur * 14 Aur J05154+3241A 57799 24504 None 33959 5:15:24.4 32:41:15.4 5.00 A9V 7670 0.00
iota Ori * iot Ori J05354-0555A 132323 26241 Hatysa 37043 5:35:26.0 -5:54:35.6 2.77 O9IIIvar 18000 0.10
gamma Lep * gam Lep J05445-2227A 170759 27072 None 38393 5:44:27.8 -22:26:54.2 3.60 F6V 6306 -0.12
h3945 CMa * 145 CMa J07166-2319A 173349 35210 None 56577 7:16:36.8 -23:18:56.1 4.79 K3Ib- 3970 0.03
iota Cnc * iot Cnc J08467+2846A 80416 43103 None 74739 8:46:41.8 28:45:35.6 4.02 G8IIIaBa0.2 4905 -0.06
24 Com * 24 Com A J12351+1823A 100160 61418 None 109511 12:35:07.8 18:22:37.4 5.02 K0II-III 0 -0.04
xi Boo * ksi Boo J14514+1906AB 101250 72659 None 131156 14:51:23.4 19:06:01.7 4.59 G7Ve+K5Ve 5410 -0.05
alpha Her * alf Her J17146+1423AB None 84345 Rasalgethi 156014J 17:14:38.9 14:23:25.2 3.06 M5Ib-II+G5III+F2 0 0.00
95 Her * 95 Her J18015+2136AB 85648 88267 None 164669 18:01:30.4 21:35:44.8 0.00 A5IIIn 0 0.00
zeta Lyr * zet01 Lyr J18448+3736A 67321 91971 None 173648 18:44:46.4 37:36:18.4 4.36 Am 7914 0.38
Albireo * bet Cyg A J19307+2758A 87301 95947 Albereo None 19:30:43.3 27:57:34.8 3.09 K3II+B9.5V 4270 -0.17
31 Cyg * omi01 Cyg J20136+4644Aa,Ab 49337 99675 None 192577 20:13:37.9 46:44:28.8 3.80 K3Ib+B2IV-V 4186 0.03
beta Cap * bet Cap J20210-1447AB None None Dabih None 20:21:00.7 -14:46:53.0 0.00 0 0.00
gamma Del * gam Del J20467+1607AB None None None None 20:46:39.2 16:07:27.0 3.91 F7 0 0.00
delta Cep * del Cep J22292+5825A 34508 110991 None 213306 22:29:10.3 58:24:54.7 3.75 F5Iab:+B7-8 5695 7.62

That is a decent start, but it does have some deficiencies. In some cases the identifier is clearly associated with a pair of objects, as can be seen from the multiple spectral types, e.g. gamma And, iota Tri, 31 Cyg. That is not quite what we want, as the positions and other data aren't for a single star. Solving that is a topic for another post...

Sunday, February 04, 2018

Fixing Windows Update problems

I've been experiencing some Windows Update problems, in particular Windows update endlessly "Checking for updates". After much trial and error I found a How-To Geek article by Walter Glenn helpful. In particular, installing and using the WSUS Offline Update was necessary before cleaning out the wuauserv cache.