Difference between revisions of "Identification of Previously Known Objects on Candidate List"
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=Thursday, 9/1, from Luisa=
=Thursday, 9/1, from Luisa=
Graphical representation of all 5 literature papers, plus ours, in BRC 27
Graphical representation of all 5 literature papers, plus ours, in BRC 27. Ogura 8 additionally indicated by large black star, since source density is high right there.
Revision as of 18:43, 1 September 2011
Friday: 08/27/2011, from Diane
Starting the conversation, here is what I sent out Friday about BRC 27.
Each SED is unique, which should mean that there are no duplications: in addition:
- Candidates 15 & 16 have the same rough coordinates, but show up as Ogura 8 & 9
- Evidently I mislabeled Ogura 21 and Ogura 22 as candidates 30 & 29.
- Candidate 29 is Ogura 21
- Candidate 30 is identified as a YSO (Chauhan) not Ogura 22 (as I had previously noted)
- Ogura 22 at 07 04 08.0 -11 23 54.75 is not on our list of candidates. (It is on the full list, but it is not one of the ones we targeted)
- Candidate 31 is NOT identified as a YSO, and is not credited to anyone I have found. this is a change from Friday
- At this point, the only candidates that are not designated as either YSO’s or stars seem to be 12, 13, and 19.
Does anybody else have an opinion on any of this?
SATURDAY, 8.28, from Diane
Clarification on the referenced excel file that I sent out on Friday;
Column B: Since one of our tasks was to determine which of these objects have been previously identified, I went to Harvard's site for Simbad
(be sure you select the Aladin applet for the US, or it will take you to France)
- npd is code for no previous designation (which is what we seem to be hunting)
For each of the candidates, I looked to see if there was any kind of identification. (You will notice that so many things are labeled, it's actually surprising to find an object that does not have one) Be sure to scroll down the the bottom of the screen to see if they have actual names; many of them are labeled Ogura.
If it says YSO, it was labeled as such on Simbad, which means somebody identified it at some point in the past... Query: That means we are confirming it?
When I could find someone to attribute a YSO to, I credited them. (see column AA) Candidates 4, 5, 11 & 28 are are not labelled on the diagram but are Ogura 3, 4, 7 & 19. Since they are in the literature, I'm not sure why they are not labeled on the image.
Objects that were cited as A's or B's, I took at face value (6,7, 10, 14, & 27). I think I understand how 27 is a blob in IRAC, but a faint point source in JHK, but why is it brighter in its R magnitude than its V magnitude? The U & B magnitudes are dimmer than the V, and I would not expect that from a B. (does that make sense?)
Candidates 29, 30, & 31 are still interesting.
Column I: anything coded yellow is something I thought was a star before I started digging. What I based that on was whether or not we had a V magnitude farther over on the table (which just happens to also be column V). I revised those opinions based on what I found in Simbad and what is in column J.
Column J: Gator DSS & 2MASS/ This brought up 5 images from DSS (information at the bottom of the column) and JHK, so I was comparing the way each object looked for the different bands.
Going through it one more time, some of my thoughts have changed, and so has the file, so it is posted above.
Today's examination has led me to the following issues:
- Is #1 really a star?
- 29 and 30 are actually a trio of objects (and I do not mean #31 as listed). I know that 31 has the same location as 30, but that is not where I find it in Simbad.
The Simbad address is 07:04:08.13 -11:23:08.7 This is a strikingly different location, and I think we need to dig further on this.
- 35 is labeled as a reflection nebula. Should we ignore it?
--Sartore 14:08, 27 August 2011 (PDT)
Mon Aug 29, from Luisa
looooooong email generalized response from luisa copied in here; see also Venn diagram attachment: File:Lmr email 29aug ppt.pdf
I did not copy in all of the subsequent mails from me, just the important bits
long email, Subject: untangling things
OK... before I start reading your mails from the last few days (which may take me a bit), let me return to the 'big picture' for a bit. Whenever tackling a big problem, I like to review both "What do we know" and "What are we trying to find". If this email is useful, I can copy this into the Wiki later.
Remember the first page of the attached? This is a Venn diagram I made for you on Friday of your visit that was meant to represent the relationship among all the various source lists we were considering. At that point in the process, we had already consolidated things into:
- All "bright enough" sources covered by the Spitzer maps (a conceptual list only)
- Sources in my catalog of extractions (I provided this)
- Sources in this general direction studied by anyone else, ever (the majority of those reported are also YSOs, but not all of them)
out of those sets, our scientific goals mean that we are aiming for a discussion of:
- YSO candidates we select from IR excess
- YSOs that others identify that do not appear to have an IR excess.
The first page in the attached was even trying to correctly represent the relative sizes of the circles in that "all bright enough sources" ought to be darn close to "sources in my catalog" and that there will be some "sources in this general direction..." not covered by the maps and some of those without IR excesses.
OK, so NOW you are going back to revisit the list of "Sources in this general direction studied by anyone else, ever" because even during your visit, we had identified some issues with that list.
On the second page of the attached, I tried to spatially represent the concepts behind what we're doing now, but I admit the circles are not as carefully constructed/laid out as the first page!
Each of these 5 papers (Ogura et al 2002, Gregorio Hetem et al. 2009, Chauhan et al 2009, Shevchenki et al 1999 and Wiramihardja et al 1986) looked in the direction of BRC27. Surely, then, they saw some of the same sources as each other, and as what we are seeing. For example, the Gregorio-Hetem survey covered a HUGE area, and we care only about a part of it. Ogura saw some of the same sources that Gregorio-Hetem did, but not all of them -- they were not covering the same areas, but even within the same area, they did not see the same sources, because one survey was x-ray driven, and one was Halpha driven. They *will* see different sources, because each survey is not infinitely deep -- the sensitivity of the surveys is limited, and as such will not see every source in this direction. Same for each other pair of papers, and our survey.
The goal here is to construct a list that is as clean as possible for each of the objects that these other folks studied, identifying which objects are truly the same between surveys, and identifying which of these objects are ones that those authors thought were young stars. We also want to carry along each of the relevant bits of information that these other authors provided -- you already know that the SED is a lot easier to identify as clearly a young object or a contaminant if there is optical data, so if the other authors reported any optical measurements, we should keep track of those and tie them to the correct object in our analysis. We should also make note of any spectral types or other relevant information. The "money question" (page 3 of the attached) is thus:
- Which objects from paper x are also seen in paper y?
and then, the next step is
- Which of these objects are seen in the IRAC data?
This would be an easy task if:
- everyone provided their original images, either as a figure or as a fits file
- everyone worked in the same coordinate system, by which i mean not just "J2000" vs "B1950" but "J2000 tied to 2MASS" as opposed to "J2000 tied to the pulsars seen by NRAO" or "J2000 as calibrated as best I can based on the HST Guide Stars I happen to see in my image" (the latter of which is what we are likely to have with the Haleakela data, by the way).
- the objects were all greater than 5 arcseconds apart from each other on the sky, such that each source that is detected was cleanly and uniquely detected in each survey.
- and, of course, that we were guaranteed a match between surveys.
Working backwards up that list...
We've already talked above about how we are not guaranteed a match between surveys, because stars are different brightnesses at different bands, and because the surveys have limited sensitivity.
You know from staring at the images that there are plenty of sources that are very close together. Even among just the YSO candidates, some are very close to each other, closer than 5 arcseconds.
If we had fabulous coordinates for everything, we could let the computer match them all up and not worry about it. But we don't. And it's not just a matter of precessing the B1950 ones to J2000 ones either - there are inherent errors in those old coordinates which will not necessarily smoothly map into a clean match to other objects.
If we had images, we could line them up by eye and identify the same objects in each frame. I don't necessarily mean "line them up in ds9" since we don't have any fits files. I mean, by comparison between images they publish and images to which you have access (IRAC, 2MASS, POSS), you can identify the objects. This is what we are going to have to retreat to, in the tough cases.
Here are some notes on these 5 papers, in no particular order:
- Gregorio-Hetem - finding charts for a few complex fields, which may or may not be in our region. J2000 coordinates tied to 2mass, though, so less worried about these. note that their discussion includes this very conceptual problem -- they are trying to tie X-ray sources to optical sources.
- Wiramihardja - no finding charts; a few very coarse-scale ones, one with just YSOs. Not a lot of help here. Also just 1950 coordinates read off a photographic plate. Likely to be large and unsystematic errors.
- Shevchenko - finding chart provided (fig 1). 1950 coordinates. big field (bigger than the region we care about).
- Ogura - finding chart provided; J2000 coordinates but not necessarily tied to 2MASS.
- Chauhan - no real finding charts provided; there are a few coarse-scale ones. J2000 coordinates tied to 2mass, though, so less worried about these.
For each of these 5 papers, we obtained a machine-readable (read as "plain text file that the computer can parse into individual numbers rather than images of numbers") version of the relevant data tables. This was either:
- obtained from the journal itself, in which case the data table is much longer than we need
- obtained from what diane did (she followed what i was telling her to do), where she typed in the coordinates of the objects in our fields from these older papers and attempted to get updated coordinates.
These tables are at the bottom of this page here: http://coolwiki.ipac.caltech.edu/index.php/BRC_Spring_work Look down under "Literature known YSOs" and then under "These papers in order of priority" and then each paper's listing has a link to files, e.g., "File:Chauhan-table3.txt".
What Diane did on my advice (see the YouTube video on that page) SHOULD work in MOST cases but did not work in every case; more on this momentarily. What she did was :
- type the 1950 coordinates into the twomass point source archive, making sure that it knows that it is 1950 coordinates.
- look at what comes back, and take the closest bright object.
Then we had 5 lists of UPDATED, HIGH QUALITY coordinates, one per paper, and we let the computer run through the list, finding the matches between papers. I then generated one file that purported to have one line per literature object, with all the relevant data on that line. But we were able to identify problems with this, in that a few sources during this process were tied to the same object, or identified in other ways as duplicates or incorrect matches.
What I recommended before that you (plural) do to get updated coordinates for targets works ON THE ASSUMPTION THAT THERE ARE NOT "TOO MANY" SOURCES NEARBY, AND THAT THE PRIOR SURVEYS, BEING SHALLOW, ARE MOST LIKELY TO MATCH TO THE BRIGHT 2MASS SOURCE. As I say, this should work in MOST cases but not ALL of them. In some cases, two distinct sources reported, e.g., two sources in Ogura were matched to the same 2MASS source during this process, and thus matched to the same IRAC source when we let the computer merge the lists.
To untangle this, we need to go back, possibly just to the duplicate sources, possibly through all of them if you can't identify with certainty which are the duplicates, and make really sure we have obtained the best possible coordinates. If the original authors are reporting more than one source within one paper, we should not consolidate them into one unless we are REALLY sure that the original authors were wrong. (This does happen; see my North American Nebula paper for examples.) Within each paper, this is what I would do:
- Go back and do the 2MASS archive search again (Go here: http://irsa.ipac.caltech.edu/applications/Gator/ -- pick 2MASS then on the next page pick 2mass point source catalog (PSC), then use that search page, making sure to specify which coordinate system in which you are working. use the coordinates from the original paper to avoid transcription errors, as opposed to any subsequent notes or xls files.)
- Look at the sources returned. Is there just one within 5-10 arcsec? that's probably your match; go on to the next source. If there is more than one, is there just one BRIGHT one within 5-10 arcsec? Is there another source from that same paper within 5-10 arcsec? If the answer to either of those questions is yes, go on to the next step.
- Go get the images in another window. Compare the images (if provided) from the original papers. We can use Finder Chart (http://irsa.ipac.caltech.edu/applications/FinderChart/) to get DSS and 2MASS images of the region where there is a confusing match. Compare this to the images provided in the papers. Identify which object is the one(s) in the paper.
- With that information, then go back to your PSC, and then use the 2MASS point source catalog to find the actual high-precision coordinates of that specific dot you have identified in the images as the match to the literature object.
Then I (or you) can take the updated high-precision lists of coordinates, merge them together, and come up with a new-and-improved list of all the previously identified objects in this region, one line per object with all the relevant information.
Then we can compare this list to our detections in IRAC. There will be some with IR excesses, and some without IR excesses.
Does this all make more sense?
Bits from other mails
Diane asked, "Are we the first to ever do SED's on these objects? (If so, that's pretty exciting, isn't it?)"
Yes, in two ways:
We're the first ones to make SEDs involving the IR for ANY of these. I don't know if Chauhan actually made SEDs or just plots, and certainly they did not do 24 um. So we're unambiguously the only ones using 24 um.
We're the first ones to DISCOVER any of the IR-selected ones not in the literature. We're the first ones EVER to care about them IN ANY WAY, so the first ones to make any plots at all, SEDs or otherwise. They might have appeared in the other people's raw data, or they may not have -- they might have just not looked like YSOs there.
This is why it's so important to really make sure that we understand which ones are in the literature. We don't want to assert that we have found new YSOs, only to have someone at the AAS meeting or someone in the journal article review process to come back and say hey, no, this is NOT a new object, you just screwed up in your literature search.
Diane asked about using Simbad's YSO classification.
BE CAREFUL because as we talked about in the Spring, Simbad is not complete nor necessarily accurate. It's good for doing an initial search or for getting pointers to the papers, but at the end of the day, you always have to go back to the original papers, and do the checks that I blathered on about in my earlier mail today. You have to compare images, finding charts, original catalogs, not just Simbad.
If it says YSO, someone at some point in Simbad tagged it as a YSO. For reasons known only to them, young stars can also be tagged: X, IR, *, Em*, BD*, red, redextreme, Y*, **, EB, HH, *inCl, *inNeb, *inAssoc, V*, V*?, pMS*, TTau*, Irregular_V*, Orion_V*, FUOr, .... the ones that really get me are YSO != *inNeb != V* != pMS* != TTau* .. there's no real distinction there. For some of the rest, you can understand historical classification, but for the most part, it's just phenomenally unclear, and linked ultimately to the whim of the person entering that particular data table. So do NOT rely on simbad for these kinds of classes either.
- There will be objects with IR excesses we discover as YSO candidates,
- there will be objects with IR excesses we REdiscover as YSO candidates that someone else identified first, and
- there will be objects someone else identified as YSO candidates that we find to not have IR excesses.