BRC Optical Ground-Based Follow-Up

Big Picture

Optical data can be incredibly helpful in weeding out garbage from our YSO selection. Remember that Spitzer is phenomenally efficient, and with just a few seconds can reach objects at the edge of the Universe. Recall the discussion in the CG4 paper, and just at a gut level how much nicer the SEDs look if we have optical data too. Recall the stuff on the Resolution page (specifically example 4) and how much high spatial resolution matters. High spatial resolution optical imaging may allow us to determine that some of these objects are actually resolved galaxies. Once we add their photometry to the SEDs, the shape of the SEDs may allow us to determine that some of these objects are actually AGN and not YSOs.

The Las Cumbres (LCOGT) Faulkes Telescope on Haleakala (specifially JD Armstrong) has kindly offered to help us get optical ground-based follow-up observations. We need to plan coherently (professionally!) for these observations to ensure we get the best quality data in the least amount of time possible. ("Ooops we screwed up" will not generally get you additional telescope time.)

Planning Observations

In order to plan for ground-based follow-up of our targets, we have many things to consider. These are the same issues, in more or less the same order, that I would consider before writing a proposal to any telescope for anything; this isn't fabricated just for you!

• Are the objects visible (ever) from the observatory(ies) to which we have access?
  • Ex 1: the CG4 object from last year is a Southern Hemisphere object, so unless you have access to a Southern Hemisphere telescope, that's not possible.
  • Ex 2: the BRC objects are Northern Hemisphere (both of them). When are they visible from the LCOGT telescope in Hawaii? See airmasses calculation below to help in answering that question.
• What filters are available at the telescope? And, which are best suited to the science we want to accomplish?
  • JD says that they have currently: Sloan u,g,r,i, Halpha, and PannStarrs z,y.
  • Any constraints on the Wien side of the SED will help us, so anything optical is scientifically helpful.
  • I have no experience with z and y.
  • While young stars are often bright in Halpha (and you know that from Ogura's papers), pretty much everything is fainter in narrow band filters (such as Halpha) than broad-band filters (such as the Sloan filters). So, anything will take much longer to detect to sufficient signal-to-noise in Halpha than in the other filters. It will take less time for us to get measurements in the broadband filters.
  • I have some experience with the Sloan filters, so I know (for example) how to convert them into the right units for addition to the SEDs. Recall the shape of a stellar SED. Assuming all of our targets are really stars, will they be brighter at u or i?
  • JD says that he is willing to do two filters for us. Which two would you do? I vote for r and i. Do you understand why?
• What is the spatial extent of sources on the sky that we care about?
  • We don't have a final list of sources yet. But recall that a single IRAC field of view is 5 arcminutes on a side, and the region that we care most about (with four IRAC bands) is basically a single IRAC field of view. There are serendipitously obtained patches of just 2 bands offset from the main field; each of those patches is also basically a single IRAC field of view, so basically also 5 arcmin on a side. The centers of the serendipitously obtained fields are both a little more than 5 arcminutes offset from the center of the main field.
• What is the spatial extent of a single pointing of the ground-based telescope?
  • In this case, 9 arcmin. So with a single pointing, we can obtain essentially the entire region with 4-band IRAC coverage in one of our fields, even if the fields are rotated nearly 45 degrees with respect to each other. So, great! No need to tile a large region with the LCOGT telescope.
• What is the surface density of the sources in our field of view, and what is the spatial resolution of the optical telescope?
  • Recall the Resolution discussion to understand why this matters.
  • The spatial resolution of IRAC is ~1.2-1.5 arcsec. There may be sources spaced closer together than that, but we wouldn't be able to tell based on the IRAC data.
  • The spatial resolution of the LCOGT telescope is 1.1 arcsec, and is seeing-limited. So, if we have a bad weather night, then the resolution will be worse, but seems to commonly be comparable to IRAC. So we're good here too.
• What are the total integration times we need?
  • JD says "magnitude 19 is easily within reach."
  • What are the brightnesses we expect from our targets? Ah, this is the meat of it! More below.
• How many dithers will be needed?
  • Typically, one does at least 3 dithers in order to clean out cosmic rays, but if the exposures are very short, just one can be sufficient. It depends on how much our total integration time works out to be.
• What kinds of calibrators do we need?
  • We need to find (stable) objects of known brightnesses in r and i bands (preferably comparable brightnesses to our targets), at a comparable airmass to our targets, and plan to observe them (request time to observe them) before and after our science targets.
  • JD says that there are some Faulkes archives of standards from which we can pick; I hope he can help with this.
• Who will actually do the observing? (and from where?)
  • No one is going to Hawaii!
  • JD says that both queue and internet-based remote observing is possible. TBD.
• In what format will we get the data back? On what timescale?
  • The images will arrive back to us in FITS format, flatfielded and bias subtracted but nothing else -- no coordinates, not calibrated, nothing else. We will need to take care of all of that in some fashion.
  • Timescale? Presumably immediately, or within a few days of the observations.
• Who will process the data (and how)?
  • You guys will have to lead this!
  • My thought was to sidestep the coordinates issue, use the IRAC images in essence as finding charts (though 2MASS might be better choices) to find the subset of sources in which we are interested (surviving best YSO candidates and calibrators in those fields), and have you guys do APT photometry on those targets. Once we have measurements in total counts (or counts/sec), we can solve for extinction and color corrections and calibrate the measured photometry (as opposed to calibrating the images themselves).

Hourly almanac (airmasses) for our targets

calculated for Hawaii.

*** Hourly airmass for brc27 ***
Epoch 2000.00: RA   7 04 00.0, dec -11 22 55
Epoch 2011.87: RA   7 04 33.4, dec -11 24 01
At midnight: UT date 2011 Nov 16, Moon 0.72 illum,  31 degr from obj
 Local      UT      LMST      HA     secz   par.angl. SunAlt MoonAlt 
 18 00     4 00    21 18    -9 47   (down)   -71.1     -4.8    ... 
 19 00     5 00    22 18    -8 47   (down)   -73.4     ...     ... 
 20 00     6 00    23 18    -7 47   (down)   -73.5     ...     ... 
 21 00     7 00     0 18    -6 46   (down)   -72.2     ...     ... 
 22 00     8 00     1 18    -5 46  (v.low)   -69.9     ...     -1.6
 23 00     9 00     2 18    -4 46    4.439   -66.3     ...     11.5
  0 00    10 00     3 19    -3 46    2.261   -61.0     ...     24.8
  1 00    11 00     4 19    -2 46    1.602   -52.8     ...     38.4
  2 00    12 00     5 19    -1 46    1.318   -40.0     ...     52.1
  3 00    13 00     6 19    -0 45    1.195   -19.8     ...     65.9
  4 00    14 00     7 19     0 15    1.172     6.7     ...     79.6
  5 00    15 00     8 19     1 15    1.240    30.7     ...     84.8
  6 00    16 00     9 20     2 15    1.430    47.0     -7.7    71.6
At midnight: UT date 2011 Dec 16, Moon 0.67 illum,  51 degr from obj
 Local      UT      LMST      HA     secz   par.angl. SunAlt MoonAlt
 18 00     4 00    23 16    -7 49   (down)   -73.5     -4.0    ... 
 19 00     5 00     0 16    -6 48   (down)   -72.3    -17.1    ... 
 20 00     6 00     1 16    -5 48  (v.low)   -70.0     ...     ... 
 21 00     7 00     2 16    -4 48    4.599   -66.5     ...     ... 
 22 00     8 00     3 17    -3 48    2.297   -61.2     ...     ... 
 23 00     9 00     4 17    -2 48    1.616   -53.2     ...      2.1
  0 00    10 00     5 17    -1 48    1.324   -40.5     ...     15.7
  1 00    11 00     6 17    -0 47    1.197   -20.6     ...     29.4
  2 00    12 00     7 17     0 13    1.171     5.7     ...     42.9
  3 00    13 00     8 17     1 13    1.236    30.0     ...     56.0
  4 00    14 00     9 18     2 13    1.420    46.6     ...     67.7
  5 00    15 00    10 18     3 13    1.830    57.0     ...     74.2
  6 00    16 00    11 18     4 13    2.884    63.7    -11.5    69.5

*** Hourly airmass for brc34 ***
Epoch 2000.00: RA  21 33 30.0, dec +58 04 32
Epoch 2011.62: RA  21 33 50.9, dec +58 07 39
At midnight: UT date 2011 Aug 16, Moon 0.93 illum,  61 degr from obj
 Local      UT      LMST      HA     secz   par.angl. SunAlt MoonAlt
 19 00     5 00    16 15    -5 19    2.653   -87.8     -3.0    ... 
 20 00     6 00    17 15    -4 19    1.997  -100.9    -16.4    -1.4
 21 00     7 00    18 15    -3 18    1.639  -115.3     ...     12.4
 22 00     8 00    19 16    -2 18    1.434  -131.9     ...     26.2
 23 00     9 00    20 16    -1 18    1.322  -151.3     ...     39.8
  0 00    10 00    21 16    -0 18    1.277  -173.2     ...     52.9
  1 00    11 00    22 16     0 42    1.288   164.1     ...     64.6
  2 00    12 00    23 16     1 42    1.359   143.1     ...     71.8
  3 00    13 00     0 16     2 43    1.504   124.9     ...     69.1
  4 00    14 00     1 17     3 43    1.760   109.2     ...     59.1
  5 00    15 00     2 17     4 43    2.212    95.4    -14.8    46.5
  6 00    16 00     3 17     5 43    3.080    82.7     -1.4    33.2
At midnight: UT date 2011 Sep 16, Moon 0.86 illum,  66 degr from obj
 Local      UT      LMST      HA     secz   par.angl. SunAlt MoonAlt
 19 00     5 00    18 17    -3 17    1.631  -115.8     -9.2    ... 
 20 00     6 00    19 17    -2 16    1.430  -132.5     ...     ... 
 21 00     7 00    20 18    -1 16    1.320  -151.9     ...      6.6
 22 00     8 00    21 18    -0 16    1.276  -173.9     ...     20.0
 23 00     9 00    22 18     0 44    1.289   163.4     ...     33.6
  0 00    10 00    23 18     1 44    1.362   142.5     ...     47.4
  1 00    11 00     0 18     2 44    1.510   124.3     ...     61.3
  2 00    12 00     1 18     3 45    1.771   108.8     ...     75.2
  3 00    13 00     2 19     4 45    2.232    95.0     ...     87.5
  4 00    14 00     3 19     5 45    3.119    82.3     ...     76.4
  5 00    15 00     4 19     6 45    5.239    70.0    -17.1    62.6
  6 00    16 00     5 19     7 45   14.754    57.7     -3.1    48.8
At midnight: UT date 2011 Oct 16, Moon 0.84 illum,  79 degr from obj
 Local      UT      LMST      HA     secz   par.angl. SunAlt MoonAlt
 18 00     4 00    19 15    -2 18    1.435  -131.9     -1.2    ... 
 19 00     5 00    20 16    -1 18    1.323  -151.2    -15.2    ... 
 20 00     6 00    21 16    -0 18    1.277  -173.2     ...     ... 
 21 00     7 00    22 16     0 42    1.288   164.2     ...      4.2
 22 00     8 00    23 16     1 42    1.358   143.1     ...     17.1
 23 00     9 00     0 16     2 42    1.503   124.9     ...     30.3
  0 00    10 00     1 16     3 43    1.759   109.3     ...     43.6
  1 00    11 00     2 17     4 43    2.211    95.5     ...     57.2
  2 00    12 00     3 17     5 43    3.076    82.7     ...     70.8
  3 00    13 00     4 17     6 43    5.122    70.4     ...     84.0
  4 00    14 00     5 17     7 43   13.931    58.1     ...     81.2
  5 00    15 00     6 17     8 43   (down)    45.4     ...     67.7
  6 00    16 00     7 17     9 44   (down)    32.1     -4.8    54.1