Subject: Thuan-Gunn photometric standards

From: James Rhoads

Submitted: Tue, 27 Jun 1995 12:29:01 -0400

Message number: 1 (previous: 0, next: 2 up: Index)

							27 June 1995
This is a more-or-less verbatim copy of something I wrote following
my 22 June run.
	Here are some references I found useful for Thuan-Gunn filter
photometric standard stars to use with DIS in imaging mode:

(0) Thuan and Gunn 1976 PASP 88:543 defines the system.  The standards
  fainter than g ~ 10.5 don't saturate the chip in a 1 second exposure
  (though this is seeing dependent); there are about 12 such stars.
  Positions are given to accuracy to 0.1 m RA and 1 min dec; not sure
  how many of the stars have large proper motions that would need to be
  accounted for-- I used BD+28 4211 and BD+17 4708, which did turn up
  where expected.

(i) Inger Jorgensen, 1994, PASP 106:967-973, "Secondary Photometric
  Standards for the Thuan-Gunn and Johnson-Kron-Cousins Systems"
  Table of some 100 standard star magnitudes, without coordinates.

  Therefore, one has to find coordinates in earlier literature cited by

(ii) Stobie et al, 1985, A&A Supp, 60:503-515, "CCD stellar sequences in
  galactic structure fields", has coordinates for two standard star
  fields, F762-9 and F1038-6, with photometry in Jorgensen.  The one I
  used, F1038-6, is at 23:31:06 +09:51:00 (1950.0) ; the other is at
  3:30:49 -06:15:30 (1950.0).  Each has 8-9 secondary photometric
  standard stars in one DIS field, with a wide range of magnitudes; 5
  seconds didn't saturate the brightest star (r=12.7) in F1038-6 but 20 sec
  did; haven't yet looked to see if I saw the faintest (r=19.2).

(iii) Four further fields in Jorgensen's table have coordinates in 
  Landolt 1992, AJ 104:340.   They are PG1633+099, at 16:35:32 +09:47:10
  (2000.0) [4 stars, r mag 12.7-15] ; Mark A at 20:43:58 -10:46:30
  (2000.0) [4 stars, r mag 13.6-15.8]; SA 92 at 00:54:41 +00:42 (2000.0)
  [6 stars, may not quite fit in 1 DIS field, r mag 13.0-15],
  and SA 110 at 18:43:09 +00:30:15 (2000.0) [8 stars, r mag 11.4-13.8].
  I used the latter, found 5 sec saturated some stars in g, 1 sec did
  not, and 2 sec would probably saturate in good seeing.
(iv) Kent's paper 1985 PASP 97:165-174 has much photometry but seems not
  to tabulate coordinates beyond the original Thuan-Gunn standards.
  Might be a useful place to continue the lit search.

That's it for now.  Please feel free to pass these along to anyone else
who might be interested; I've tried to be careful with the above
coordinates but can't absolutely guarantee no errors.
                            James Rhoads  (
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