Difference between revisions of "Getting your feet wet with catalogs and plots at IRSA"
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Revision as of 22:39, 16 May 2022
Based in part on Gliese Catalog Explorations, this activity suggestion works with the Gliese-Jareiss catalog to (a) get comfortable with working with catalogs and plots at IRSA and (b) explore an optical color-magnitude diagram, as well as using SIMBAD.
This PASP paper presents an updated version of the Gliese-Jareiss catalog of nearby stars. In order to get this source list into IRSA tools, you need to get it into IPAC Table Format, which is just ASCII but it has to have the right formatting. If you get it "close enough" to IPAC table format, you can pass it through IRSA's IPAC Table Validator which can make formatting corrections. [Here] is the IPAC table I constructed from these sources. I don't know if the wiki will preserve the formatting of that sufficiently, so you may wish to save it, make sure it has a .tbl extension, and pass your copy through the Table Validator to be safe.
(The positions in that catalog should be pretty good; they come from 2MASS, so they are J2000. However, these stars are often close enough that they have a high enough proper motion that they may have moved enough that finding a match automatically may be hard!)
Go to the IRSA Catalog Search Tool, pick Gaia DR2 (or EDR3 if it’s out by the time you get to this), do a multi-object search, 1-to-1 matching with a 5 arcsecond radius, and upload this list of sources (saved as an IPAC table file with the extension .tbl).
Make a color-magnitude diagram! You can put G (phot_g_mean_mag) on the y-axis (don’t forget to reverse the y axis to put bright objects at the top) and either the field bp_rp (which is B-R) or explicitly “phot_bp_mean_mag-phot_rp_mean_mag” on the x-axis. Look at that CMD. But wait! You can do better.
Because you have matched to Gaia data, you now have distances to these stars, so you can do more than just make a color-magnitude diagram; you can make a color-absolute magnitude diagram! However, parallax is tabulated, not distance. Note that the parallax is tabulated in units of milliarcsec (mas). Because the IRSA plotting can do simple mathematical manipulations including logarithms, you can use the information there to make an absolute color-magnitude diagram. (Use phot_g_mean_mag- (5*log10(1000/parallax) - 5) for the y axis, and don’t forget to reverse the y axis to put bright objects at the top. For the x axis, use either the field bp_rp (which is B-R) or explicitly do the subtraction with phot_bp_mean_mag-phot_rp_mean_mag.) Look at how much better your diagram looks when you take distances into account! The scatter goes way down on the main sequence, and the giants and white dwarfs differentiate themselves much more clearly.
Science: Which stars are white dwarfs in your diagram? Which stars are giants in your diagram? Click on any white dwarf. The star corresponding to the point in the plot is highlighted in the table. Identify that source in the list. Copy its name. Go to another browser tab/window and go to Simbad. Search by identifier, paste in the name, and search. Does Simbad think that target is a white dwarf? If it can’t find the object by name, copy the position and search by position. If you use a large search radius, it might give you a list of sources. If it does that, then the list it gives you is sorted by position, and the source closest to your position is at the top of the list, so the first source on the list is likely to match the position you gave it.
Extension: scroll down and find the references on the object. Ask it to give you the reference list. Find the most recent paper that mentions this object. Is it a paper about Gaia observations of white dwarfs? What is it telling you about this target? Do it again for another white dwarf.
Repeat for any red giant.
- Filter the catalog. How many of the stars don’t have matches in Gaia? What happens to the fraction that is matched if you change the 1-to-1 matching radius to something larger or smaller? What are the risks of just setting the matching radius to 15 or 20 arcsec?
- Sort the catalog. Which is the closest/furthest star from us in the list? Caution: The column near the left that has "dist" in it is not the distance of the source to us. What do you think that distance column actually mean? hint: the second column near it is position angle. In order to answer the "closest/furthest" star question, you will need to use the parallax column. Is Alpha Cen or Proxima Cen in the list?
- Where does the closest star with G, B, and R end up in the observed CMD? In the absolute CMD? Are they giants or dwarfs?
TOUGH Challenge, tougher than I meant for it to be originally: How might you find main sequence binaries in this catalog?
Possibly relevant IRSA videos (links may be out of date; if they are, there should be a more recent one with a similar name in the IRSA YouTube feed):
- https://youtu.be/xy97_aT8Jx0 introduction to plots
- https://youtu.be/IGQB8a4YY4U making more sophisticated plots
- https://youtu.be/vZOIJR3-StY catalog query: one-to-one matching
- https://youtu.be/CaNhqcdlVFU catalog query overview
Goal: Compare color-mag and color-color diagrams for the young stars in Taurus and the Gliese-Jareiss catalog of nearby stars to see how different they are. (Hint: they are very different in many cases!)
Do the prior activity to get Gliese-Jareiss catalog matched to Gaia and loaded into one IRSA Catalog search window. Get the Taurus catalog from here -- my version is here but you will have to do the same tricks you did above to ensure the formatting and filename are both right.