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[vsnet-chat 1361] A2.0 photometry
- Date: Tue, 6 Oct 1998 17:21:03 -0700
- To: aavso-discussion@mcmaster.physics.ca, bmarsden@cfa.harvard.edu, dgm@nofs.navy.mil, francois@simbad.u-strasbg.fr, loneos@lowell, mplist@bitnik.com, vsnet-chat@kusastro.kyoto-u.ac.jp
- From: bas@lowell.Lowell.Edu (Brian Skiff)
- Subject: [vsnet-chat 1361] A2.0 photometry
- Sender: owner-vsnet-chat@kusastro.kyoto-u.ac.jp
Folks,
I've made some comparisons of the new USNO-A2.0 magnitudes against a
sample of faint sequence stars in various places in the sky. This was to
test whether one can use the A2.0 magnitudes for zero-point determinations
for wide-field imaging, for "instant" comparison sequences for variables
stars, and so on. The faint stars with BVR photometry were selected from the
large file I keep at:
http://ftp.lowell.edu/pub/bas/starcats/loneos.stds
The star-by-star comparison is shown below (the list is more than 80
columns wide). The coordinates come mostly from A1.0, so may differ
somewhat from the new catalogue. The columns on the far right show the
differences against the "standards" (some of them really are bona fide
standards) in the sense of "A2.0 minus reference", so that if the offset
is negative, then A2.0 is too bright.
As is readily apparent, compared to Cousins R, the A2.0 red magnitudes are
pretty consistently too bright; A2.0 blue versus B is also too bright. This
seems to be independent of brightness (in the range 12 < mag < 21), low- or
high-latitude, northern/southern hemisphere---but very inconsistent from
field-to-field. From the crowded fields near M13, M92, and Nova Ophiuchi 1998,
one can say that sometimes crowding is probably causing problems. But there
are zero-point offsets even where there are well-established sequences at
high galactic latitude along the Equator or in the southern Cousins/Graham
E-regions.
In brief, A2.0 does not solve the perennial problem of having reliable
photometry for lots and lots of faint stars anywhere in the sky. This was not
Dave Monet's aim in building the catalogue, but many observers will make
unwarranted assumptions about the data. Be careful!
\Brian
++++++++++++++++++++++++++++++++++++
Name RA (2000) Dec V B-V V-R mr mb del-r del-b
Bobby Bus' Chiron calibration
SJB c01-05 0 16 18.0 +5 07 49 17.83 0.70 0.40 17.2 18.1 -0.2 -0.4
SJB c01-11 0 16 18.4 +5 03 41 17.68 0.92 0.49 16.8 18.3 -0.4 -0.3
SJB c01-02 0 16 24.8 +5 07 49 16.21 0.96 0.55 15.6 16.8 -0.1 -0.4
Graham's sequence around NGC 300
NGC 300 21 0 54 15.0 -37 54 31 19.79 1.42 0.95 18.1 20.2 -0.7 -1.0
NGC 300 28 0 54 20.3 -37 53 23 20.61 1.52 1.20 18.1 20.5 -1.3 -1.6
NGC 300 13 0 54 21.2 -37 55 03 17.58 0.52 0.32 16.8 18.0 -0.5 -0.1
NGC 300 12 0 54 28.8 -37 56 24 16.04 0.61 0.36 15.2 16.8 -0.5 0.2
NGC 300 11 0 54 31.4 -37 54 53 15.27 0.98 0.52 14.2 16.3 -0.6 0.1
SAAO group
SGP 5 0 56 48.9 -27 39 20 17.23 0.76 0.51 16.9 17.7 0.2 -0.3
SGP 8 0 56 56.6 -27 37 02 18.13 1.17 0.84 17.3 18.3 0.0 -1.0
SGP 26 0 56 47.7 -27 36 17 19.15 1.48 1.11 17.8 19.4 -0.2 -1.2
SGP 15 0 56 43.5 -27 37 10 19.92 1.65 1.34 18.0 20.2 -0.6 -1.4
SGP 21 0 56 51.6 -27 37 08 21.05 1.77 1.27 17.6 21.4 -2.2 -1.4
Calan/Tololo SN group sequence
MCG -06-04-14 c8 1 21 56.0 -34 12 24 19.93 0.82 0.40 17.8 19.2 -1.7 -1.6
MCG -06-04-14 c7 1 21 56.5 -34 13 51 16.37 0.54 0.37 17.5 20.4 1.5 3.5
MCG -06-04-14 c4 1 22 00.2 -34 11 27 19.20 1.50 0.94 17.8 19.7 -0.5 -1.0
MCG -06-04-14 c3 1 22 01.1 -34 13 29 19.37 0.52 0.37 17.9 19.2 -1.1 -0.7
Henden BVRI, near SA 100
smspbn-029 8 48 48.5 +1 14 51 14.90 0.81 0.43 14.4 15.4 -0.1 -0.3
smspbn-008 8 49 04.6 +1 19 13 15.49 0.81 0.50 14.9 16.2 -0.1 -0.1
smspbs-009 8 49 46.3 -1 10 57 17.05 1.19 0.70 16.1 17.8 -0.3 -0.4
smspbs-062 8 50 04.8 -1 18 10 16.74 0.64 0.38 16.1 16.7 -0.3 -0.7
Kron et al NGP sequence
SA 57-8303 13 09 12.7 +29 20 20 18.36 1.04 0.67 17.4 19.0 -0.3 -0.4
SA 57-9801 13 09 07.8 +29 22 28 18.92 1.19 0.75 17.7 19.2 -0.5 -0.9
Zickgraf and Humphreys sequence
NGC 5128 Z1 13 25 49.4 -42 44 29 14.23 0.67 0.37 13.1 15.9 -0.8 1.0
NGC 5128 Z5 13 25 46.5 -42 44 38 17.58 0.88 0.49 16.5 18.4 -0.6 -0.1
NGC 5128 Z6 13 25 44.0 -42 43 10 18.11 0.55 0.35 17.3 18.5 -0.5 -0.2
NGC 5128 Z9 13 25 46.4 -42 43 37 19.18 1.03 0.69 17.8 19.5 -0.7 -0.7
Landolt field
PG 1633+099A 16 35 26.0 +9 47 53 15.26 0.87 0.51 14.4 15.5 -0.3 -0.6
PG 1633+099B 16 35 33.3 +9 46 21 12.97 1.08 0.59 12.1 13.8 -0.3 -0.3
PG 1633+099C 16 35 37.3 +9 46 16 13.23 1.13 0.62 12.1 13.9 -0.5 -0.5
PG 1633+099D 16 35 40.1 +9 46 42 13.69 0.54 0.32 13.0 14.0 -0.4 -0.2
Dawson & Forbes sequence
M13 AJ21 16 41 20.1 +36 30 50 16.17 0.74 0.43 14.0 14.5 -1.7 -2.4
M13 AJ62a 16 41 20.7 +36 22 53 16.22 0.71 0.41 15.5 15.8 -0.3 -1.1
M13 AJ45 16 41 02.6 +36 26 15 15.01 0.80 0.47 14.2 14.5 -0.3 -1.3
M13 AJ2 16 41 05.1 +36 28 21 14.73 0.85 0.47 13.9 14.7 -0.4 -0.9
KPNO consortium sequence
NGC 6341 IX-10 17 17 04.0 +43 02 03 14.63 0.78 0.49 13.9 15.1 -0.2 -0.3
NGC 6341 IX-8 17 16 58.1 +43 02 34 16.35 -0.11 -0.04 16.3 15.9 -0.1 -0.3
NGC 6341 B 17 17 04.7 +43 02 58 16.81 0.63 0.40 16.2 16.8 -0.2 -0.6
NGC 6341 IX-100 17 17 00.3 +43 02 44 17.01 1.14 0.72 16.3 17.7 0.0 -0.5
Henden BVRI
Nova Oph 1998 08 17 31 59.8 -19 14 31 14.10 0.96 0.61 12.8 15.0 -0.7 -0.1
Nova Oph 1998 10 17 32 02.7 -19 15 46 14.70 1.78 1.02 14.3 16.7 0.6 0.2
Nova Oph 1998 16 17 31 59.9 -19 14 13 15.64 0.94 0.61 15.2 16.3 0.2 -0.3
Nova Oph 1998 17 17 31 57.8 -19 13 26 16.31 1.54 0.89 16.1 17.7 0.7 -0.2
Graham E-region standards
Graham E9 k 22 45 44.5 -44 30 21 13.96 0.54 0.31 14.0 13.5 0.4 -1.0
Graham E9 n 22 45 30.9 -44 29 43 14.71 0.56 0.34 15.0 14.3 0.6 -1.0
Graham E9 q 22 45 25.7 -44 27 47 15.20 0.69 0.38 15.3 15.0 0.5 -0.9
Graham E9 s 22 45 42.2 -44 24 41 15.57 0.52 0.34 15.7 15.3 0.5 -0.8
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