LLAMMa Bigger Picture and Goals

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The big goal

Most succinct:  We will be looking for new candidate young stars in Ceph C using X-rays, optical, and IR data. 


More words:  There is a star forming region within the Cep OB3 molecular cloud called Ceph C. It has not been well-studied to date. Our goal is to find new candidate young stars in this region. We have data from:

  • SDSS (optical, ugriz bands, which is 0.29 to 0.90 um)
  • 2MASS (near IR, JHK bands, 1.2 to 2.2 um)
  • Spitzer/IRAC (mid IR, [3.6], [4.5], [5.8], [8], which is 3.6, 4.5, 5.8, and 8 um)
  • Spitzer/MIPS (mid IR, [24], [70], [160], which is 24, 70, and 160 um, though we may only have viable point sources in 24 um)
  • WISE (mid IR, 3.4, 4.6, 12, and 22 um)
  • Chandra (X-rays)
  • and maybe Akari (9 and 8 um) - we will need to think about this one.
  • There is Herschel data too -- PACS is 70, 100, and 160 um and SPIRE is 250, 300, and 500 um.
  • We have Halpha data from the literature, as well as SCUBA 450 and 850 um data from the literature.

We will use the 2MASS+IRAC+MIPS to identify objects that have colors consistent with being young stars. We will use the X-rays to identify other young stars that don't have strong IR excesses. We will spend a lot of time looking at images where we can to make sure that we are identifying the same object across 2 orders of magnitude in wavelength (0.29 to 24 um). We will construct SEDs to (a) be sure that we are identifying the same object across 2 orders of magnitude in wavelength, and (b) to identify objects that have SEDs consistent with being young stars (the IR color selection only uses IRAC+MIPS+2MASS, but we have a lot more data, so we ought to be able to make a better assessment). We will make color-color and color-magnitude diagrams to make sure that the objects appear in the right color spaces to be young stars.

This is in support of another study that monitored young stars in the mid-IR (3.6 and 4.5 microns) to study how young stars vary in the IR. It is very difficult/impossible to interpret some of these IR light curves without the rest of the SED to help understand the nature of the underlying YSO. This is why it's important to look for high-quality YSO candidates, and not just let the computer select them without checking them.


  • YSO = young stellar object
  • point source = a single source as recorded by the telescope+detector, as opposed to extended emission from nebulosity. The apparent size of the point source in the image is a result of the telescope+detector's spatial resolution, the brightness of the source, and the stretch used for the display. But, it is not a cloud of fuzzy emission.
  • photometry = quantitative measure of an object's brightness in a particular filter bandpass
  • filter bandpass = range of light let through to hit a detector
  • light curves = photometry of an object as a function of time
  • order of magnitude = factor of 10.  Something that costs $10 is an order of magnitude more expensive than something that costs $1. We have wavelengths that range over basically a factor of 100 here - 0.29 to 24 um.

The concrete goal

We have to come up with a science poster (and an education one) for the AAS in Jan 2017. BUT because the posters can be simple or complex, this goal is a little squishy, perhaps squishier than you might be comfortable with. What I describe here (and elsewhere on the wiki) is the kind of goal I would give a grad student. But getting through even a part of it (rather than all of it) is still a success!! This may be hard to really internalize, but it's true.

The overall "story arc"

(this is a very high level description)

OK, so I've done this a few times before. :*) There are four potentially useful pages on the wiki with the "overall story arc" or "to-do list" describing the major tasks we have to accomplish towards actually reducing our data and analyzing it. The Working with L1688 page (from 2008) tries to explain the 'story arc' by using a cluster similar to the ones we were studying to demonstrate the tasks. The Working with CG4+SA101 page (from 2010) goes through the actual region that that group studied. The more recent Working with the BRCs page (from 2011) goes through those two regions that that group studied. From 3 years ago, Working with the C-WAYS data page (from 2012) started out trying to help that team make it through all three regions, but we decided mid-summer-visit to limit our work to just BRC27. That work was continued in the following year in the Working with the C-CWEL data page. There are echoes of that work in Working with the HG-WELS data but that project is working with IR excesses at the end of the stars' lives, rather than the beginning. Last year (2015), I returned to looking for YSOs, so there is a Working with the IC 417 data page. I found that being concrete was better than being abstract, so there will be a Working with the LLAMMa data page that will be fully updated when we get to that point.

The important part is that there are lots of exit ramps off this particular highway. If we get through only a few of those tasks, but you really understand them, that's fine! If we get through them all, that's fantastic. I expect we as a group will get most of the way through them before we have to write the poster.

The overall process

  • We will start with the 2MASS+Spitzer catalogs in the region of interest.
  • We will (technically have already) run Rob Gutermuth's selection algorithm on the Spitzer+2MASS catalog, which picks things based on colors. What information I currently have to explain this selection algorithm is here: http://coolwiki.ipac.caltech.edu/index.php/Gutermuth_color_selection and in a ppt I will share on a telecon. This process will identify a subset of objects in which we will be more closely interested, e.g., a set of IR-selected YSO candidates.

Somewhat separately, on somewhat of a parallel track:

  • We will assemble the catalogs obtained from the literature and archives.
  • We will assemble a big catalog of "everything we know" about every point source in this region that we can identify. We will identify a subset of objects in this catalog that any of these folks have ever identified as a high-confidence (e.g., confirmed) YSO or a YSO candidate, e.g., a set of literature-identified YSOs and YSO candidates. But we will also have, at this point in the process, a merged catalog of everything (not just YSOs) at multiple wavelengths from prior studies, assuming they published a list of more than just the YSO candidates (and some of them have).
  • We will merge these two catalogs ("everything in the literature" and "things Rob picked as YSO candidates") such that we can do, at the very least, the following:
    • identify which of the YSOs/candidates from the literature were also recovered by Rob's selection algorithm
    • identify which of the YSOs/candidates from the literature were NOT recovered by Rob's selection algorithm
    • identify which objects (not necessarily YSOs) from the literature that were recovered by Rob's selection algorithm (we want to identify additional bands beyond the 2MASS+Spitzer data that we can add to the SED to help us decide if each of the YSO candidates identified by Rob's method are legitimate and worth keeping as YSO candidates.)
    • identify which of the X-ray sources that don't have an IR excess are likely to also be YSOs, and add them to the pile.

Portions of this process, for reasons I only sort of understand (otherwise I would fix it), is perennially confusing. Just about everyone, every year, has a terrible time keeping straight what is a "complete" catalog of "everything" in the region, what is a catalog of just literature YSOs/candidates, what is a catalog of just IR-selected YSO candidates, and the fact that "objects of interest" consist of the IR-selected YSO candidates PLUS the literature YSOs/candidates. I will keep repeating this again and again and some of you will still be confused. So please just keep asking until it makes sense!

OK, so now at this point in the process, we will have a catalog of "everything we know" about "everything of interest" in this region.

  • Now, we need to inspect each of the objects of interest to see if we can understand more about the nature of these objects. This process is necessarily recursive and will probably not end up being linear.
  • For each of these objects, we need to:
    • inspect the object in as many images, from as many bands, as we can access. Does it look like a point source in all of them? If yes, keep; if no, drop.
    • inspect where each object falls in as many CMDs/CCDs as feasible to check. Does it fall in the right place to be a YSO in this region, at this distance? If yes, keep; if no, drop.
    • construct an SED for the object using as many bands as we can access. Does it look like a YSO SED? If yes, keep; if no, drop.

There will be shades of grey here. There will be, most likely, at least the following categories for each of the "if/then" statements above: keep!, keep, keep?, drop?, drop, drop! We will discuss many if not all of them until we agree. There is an easy way to get POSS+2MASS+WISE images all at once for each object. We will have to separately inspect the images at other bands (including Spitzer) because there is no unified tool for this. Constructing SEDs will take some effort for at least the first few, but I will help turn the crank and do all of them for you.

The timeline

At our workshop in January, I talked about a global timeline for an entire NITARP project. Look here for a document very similar to the document I distributed at the January workshop. IMPORTANT NOTES: (1) This is a schedule in the ideal case. Your mileage may vary. (2) This includes everything for the entire cycle, including applications, so that I can give it to other people and have the entire thing make sense.

The important dates are:

  • Jan-Mar - proposal prep
  • Apr-June - background work
  • June-Aug - summer visits, learn and start analysis
  • Sep-Oct - continue analysis
  • Oct? - AAS abstracts due
  • Oct-Nov - finish analysis
  • Dec - write posters
  • Jan - present them!