Working with the HG-WELS data

This page is similar in concept to the summer visit pages for my prior teams (Working with the C-CWEL data; Working with the C-WAYS data page; Working with the BRCs; Working with CG4+SA101 page; Working with L1688) HOWEVER, this page was developed and updated specifically for the 2014 HG-WELS team visit. Because this team has a very different science goal, it is very different, for the most part, than these other pages.

Please note: NONE of these pages are meant to be used without applying your brain! They are NOT cookbooks! This is presented as a linear progression because of the nature of this page, but we have already done some things "out of order", and moreover, chances are excellent that you will go back and redo different pieces of this at different stages of your work.

Assembling our initial catalog

DONE but kept here for reference because it is easy to forget. LET'S DISCUSS THE QUESTIONS BELOW.

We assembled our catalog in the spring from three sources:

• de la Reza's published catalog - biased towards sources bright in the IR
• Carlberg's published catalog - much less biased set of giants assembled without regard to IR or Li, spanning range of vsini
• Carlberg's private communication set of objects mentioned in the literature as Li rich (some of which subsequently vanished from de la reza's papers)

We have a list of 196 unique objects that we assembled, keeping track of where the source was listed. Some objects are listed in more than one of those three places.

Relevant links:

• How can I find out what scientists already know about a particular astronomy topic or object?
• I'm ready to go on to the "Advanced" Literature Searching section
• HG-WELS Bigger Picture and Goals

Questions for you

• Why is it important to keep track of which stars came from which of these samples?
• Why do we not need to assemble more stars from other places? (Both scientific and practical reasons!)

Assembling other data from large catalogs

Luisa did this in its full glory but we need to do a few as a check and so you understand what I did...and so you can do it yourself later on your own for other projects.

Relevant links:

• How can I get data from other wavelengths to compare with infrared data from Spitzer? - though that wiki page focuses more on imaging. We need photometry.
• FinderChart at IRSA
• IRSA in general
• Catalog search at IRSA IMPORTANT AND NEW TO YOU
• Resolution - spatial resolution matters!
• HG-WELS Resolution Worksheet - the worksheet we did in the Spring
• Vizier
• YouTube Video Tutorial from IRSA about catalog searches

More words: Several surveys with archived data covered the whole sky. There are other surveys that just covered part of the sky. We are trying ultimately to determine if these sources have infrared (IR) excesses. We would like to assemble data from as many places as we can to flesh out the SEDs between optical (V-band) and 100 microns (the longest IRAS wavelength). As we spelled out in the proposal, the meat of what we are likely to use is probably going to be WISE 1 and WISE 4, or possibly K and WISE 4. But, as we will see below, having additional data can REALLY help us to assess whether or not we believe the two bands we will use to determine whether or not our sources have IR excesses.

1. Get from your email (or assemble yourself) an IPAC table file with all our targets and their positions in decimal ra/dec.
2. Go to the catalog search at IRSA
3. Ultimately, for this portion of the process, you will want to assemble source lists from 2MASS, WISE, and IRAS. (For the record, I did these plus many more -- those, plus Akari, Denis, both PSC and FSC from IRAS, MSX, SEIP, and certain bright objects by hand in Vizier.) Pick one of 2MASS, WISE, and IRAS to start with.
4. Do a multi-object search using that IPAC table file. Make sure to use 1-to-1 matching -- this option finds the source closest to your search position within your given search radius, and returns one line per object, even one line for those things that did not find a match. This greatly helps with the next steps.
5. Look at what it gives you in response to your search. It comes up with a plot of distance to your source as a function of source number. Why is this important? Is there a place in the list where it gets much worse? Why is this?
6. Save the output of the search to a file. Rename it and put it someplace you can find it.
7. Circle back and repeat for the rest of 2MASS, WISE, and IRAS. You will need a smallish radius for 2MASS and a largish radius for WISE and IRAS. (I used, I think, 5 arcsec for 2MASS and 20 arcsec for WISE and IRAS.)
8. Note that, as long as you use the same input tbl file every time and choose 1-to-1 matching every time, there is always the same number of lines in the output file. This makes matching across catalogs very easy. Note that all catalogs return the same columns (source name, input ra/dec, matched source id, matched source ra/dec), as well as a wide variety of additional columns. Identify the columns out of these catalogs that you actually need. (Work with the group to identify which columns you need. Hint: the photometric measurements, the errors on them, and the phot quality flags.)
9. Start an Excel file. Read in one of the search results tbl files. Delete the columns you don't need. Repeat for the other search results tbl files. Copy and paste very carefully to match the same source across all the catalogs into one Excel sheet, such that in the end you have one row per object with all the relevant resulting information you have discovered about these sources. Save often! This process is sometimes called "bandmerging" because it is merging across bands (wavelengths).
10. Spot check some sources. Are there sources bright at all bands?

Questions for you (in addition to the ones embedded above):

1. Why does resolution matter?
2. How will this process fail, if/when it fails?

Checking that the coordinates and photometry make sense, part 1 - image inspection

DONE -- at least a first pass.