Photometric Standards

Observations of standard stars are routinely acquired to enable the photometric calibration of science data, as well as to monitor the performance of the network’s telescopes. The data from these observations are available to all in the Science Archive. The proposal code for these observations is “Photometric standards”. In the image headers, the observations have OBSTYPE = STANDARD, so the BANZAI-processed file names have a “s91” suffix, rather than the “e91” given to OBSTYPE = EXPOSE.

Scheduling

Observations of standard stars are attempted every night with every imager.

  • Standard star observations are scheduled during morning astronomical twilight, i.e. from solar altitude = -12° to -9°.
  • Standard star observations are inserted into gaps in the scheduling of science observations. To make the scheduling flexible, the observation durations are short: only two filters per observation per night are scheduled. The actual duration depends on which filters are selected.
  • Observations with Johnson-Cousins (UBVRI) and Sloan (u’g’r’i’zs) filters are scheduled on alternating nights. The default exposure times are as follows:
    • Johnson-Cousins: U = 180s, B = 90s, V = 60s, R = 60s, I = 60s.
    • Sloan: u’ = 160s, g’ = 80s, r’ = 60s, i’ = 60s, zs = 80s.
  • Requests for observations of standard stars outside of the fields in the table below should be submitted to LCO's Science Support.

Standard Fields

All of the routinely observed standard star fields are found in the collection assembled by Landolt (1992) and augmented by Landolt (2009). The RAs and DECs given in the table below indicate the field center coordinates in J2000.0 of the 10’ x 10’ field-of-view of the Spectral cameras.

Name RA (deg) DEC (deg) RA (hms) DEC (dms) Season start Season end
L92 13.83912495 +0.764861 00:55:21.39 +00:45:53.5 Aug Nov
SA93 28.71708 +0.76181 01:54:52.0992 +00:45:42.516 Sep Dec
L94 44.5887255 +1.1848583 02:58:21.2941 +01:11:05.49 Oct Dec
L95 58.2189165 -0.01496 03:52:52.54 -00:00:53.856 Nov Jan
SA95 58.76535 +0.05742 03:55:03.684 +00:03:26.712 Nov Jan
RU149 111.06405 -0.54664 07:24:15.372 -00:32:47.904 Dec Mar
SA101 148.7166 -0.38300 09:54:51.984 -00:22:58.8 Feb Apr
SA103 179.2083 -0.4500 11:56:49.992 -00:27:00 Mar May
L104 190.545555 -0.5438583 12:42:10.9332 -00:32:37.89 Apr Jun
L107 235.02156 -0.33718 15:40:05.1744 -00:20:13.848 May Aug
SA108 249.34995 -0.56390 16:37:23.988 -00:33:50.04 May Jul
SA109 266.18745 -0.41700 17:44:44.988 -00:25:01.2 Jun Aug
L110 280.599 +0.19500 18:42:23.76 +00:11:42 Jun Aug
SA112 310.755 +0.1700 20:43:01.2 +00:10:12 Jul Sep
L113 325.19745 +0.47642 21:40:47.388 +00:28:35.112 Aug Oct
SA114 340.38 +0.1700 22:41:31.2 +00:10:12 Aug Oct

In the table below, the column showing “Common standards nearby” lists UBVRI + ugriz standard stars that may be included in the larger (26’ x 26’) field-of-view of the Sinistro cameras.

Name UBVRI standards ugriz standards Common standards Common standards nearby
L92 SA92-339 SA92-342 SA92-342 SA92-263
SA92-342 SA92-282
SA92-345 SA92-288
SA92-347 SA92-502
SA92-348
SA93 SA93-333 SA93-333 SA93-333 SA93-317
SA93-424
L94 SA94-702 SA94-702 SA94-702 SA94-242
SA94-251
L95 SA95-15 SA95-96 SA95-96 SA95-132
SA95-16 SA95-142
SA95-96 SA95-149
SA95-97 SA95-190
SA95-98 SA95-193
SA95-100 SA95-218
SA95-101 SA95-236
SA95-102
SA95 SA95-132 SA95-132 SA95-132 SA95-96
SA95-137 SA95-142 SA95-142 SA95-149
SA95-139 SA95-190
SA95-142 SA95-193
SA95-218
SA95-236
RU149 RU149-ABCDEF RU149-BDF RU149-BDF
SA101 SA101-315 SA101-315 SA101-315 SA101-207
SA101-316 SA101-316 SA101-316
SA103 SA103-526 SA103-526 SA103-526
SA103-626 SA103-626 SA103-626
L104 SA104-335
SA104-444
L2
L107 SA107-484
SA107-602
SA107-611
SA107-612
SA107-614
SA107-626
SA107-627
SA107-636
SA107-639
SA107-640
SA108 SA108-475 SA108-475 SA108-475
SA108-551 SA108-551 SA108-551
SA109 SA109-199 SA109-71
SA109-231
SA109-381
SA109-537
L110 SA110-349 SA110-232
SA110-355 SA110-340
SA110-358 SA110-499
SA110-360 SA110-503
SA110-361
SA112
L113 SA113-337 SA113-339 SA113-339 SA113-259
SA113-339 SA113-260
SA113-342 SA113-339
L1 SA113-466
SA113-475
SA114

Figure 1 from Smith, et al. (2007) showing the locations of ugriz (asterisks, squares) and UBVRI (circles) standard star fields.