Saturday, July 11, 2020

Comet 2020 F3 (NEOWISE)

The long period comet C/2020 F3 (aka NEOWISE, named after the satellite that first detected it) is one of the most impressive comets in the last few decades.

Although my attempts to see it personally have so far been frustrated by cloud and lack of clear sight lines to the north-east, I have been following the images of it that have appeared in Astronomy Picture Of The Day (APOD). Most if not all of the images posted so far, or presented in pop sci articles online fail to tell you any quantitative details about what you're looking at, so I decided to work out some rough distances and sizes based on the JPL Small Body Database info on NEOWISE, and the image taken from the ISS on July 5th 2020, and the kstars desktop planetarium software.

This image is a cropped, resized and annotated version of the ISS image posted at APOD on July 10, 2020. I've labelled some of the prominent stars, although to a ground-based amateur observer the star Capella, which is hidden behind parts of the ISS off the top left of the image, would be the most most prominent star visible.

From the JPL SBDB we can find that NEOWISE was about 0.3 AU from the Sun on 7/5/2020, and about 1.1 AU (approx 165 million km) from Earth. At a distance of 1.1 AU an angular distance of 1 degree is about 3 million km.

Comet C/2020 F3 (NEOWISE) as seen from the ISS on 7/5/2020
My annotated version of APOD from 07/10/2020, Image Credit: NASA, ISS Expedition 63

The angular distance between Theta Aurigae and Elnath is approximately 10.54 degrees, and the angular distance between Elnath and Kabdhiliinan (Iota Aurigae) is approximately 7.76 degrees based on using a measuring tool in kstars. If we assume the ISS image is not significantly distorted then we can measure the number of pixels between the stars on the image and compare that to the length of the tail in the image to work out its angular size. In fact the image does seem to be be slightly distorted, but taking an average I get that the visible tail in this image is about 1.7 degrees long, so the visible tail is about 5 million km long. Its not every day you can go out and see something 5 million km in size!

Sunday, February 09, 2020

NASA Astrophoto Challenge for Winter 2019 is M82

Noted with approval: the NASA Astrophoto challenge for Winter 2019 is my old friend Messier 82. See if you can create a press-release worthy image of M82 using either existing NASA images for different orbiting observatories and/or ground-based optical images taken at your request by Harvard's MicroObservatory service.

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.