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Date: Wed, 15 Dec 93 01:17:39 MST
From: bas@lowell.edu (Brian Skiff account lowell)
Subject: Magnitude sequences for VZ Aqr and HP And
This article was submitted to the Journal of the AAVSO this past August.
It may not see the light of day there for quite some time, so here it is in
case anyone can use the results.
\Brian
*****************************************************************
Photometry of Stars in the Region of VZ Aquarii and HP Andromedae
Brian A. Skiff
Lowell Observatory
1400 West Mars Hill Road
Flagstaff AZ 86001-4499
e-mail (Internet): bas@lowell.edu
Abstract
Photoelectric V and (b-y) observations of ten stars in the fields of two
dwarf novae, VZ Aqr and HP And, are presented.
1. Introduction
These fields were observed at the request of AAVSO chartmaker Charles
Scovil. The observations of stars near VZ Aquarii were done as a check on
an existing sequence, while no stars were previously available for the area
around HP Andromedae.
2. Observations
The observations were made with the Lowell 53cm photometric telescope,
located on Mars Hill, Flagstaff, Arizona. A single-channel photoelectric
photometer fitted with Stromgren uvby filters is permanently mounted on the
telescope. The observations were made on 1992 August 6, 25, and 26 UT.
Measures were made through the y and b filters of the four-color system; the
y measures were transformed to Johnson V, as is usual. A diaphragm 19-arcsec
diameter was used.
The standard stars were measured before and after the observations of
the AAVSO chart fields. After correcting for extinction, the instrumental
magnitudes for the standards were fit with a linear least-squares solution
including a color term. The averaged results for the standard stars on the
three nights are summarized in Table 1. The stars are listed in RA order,
and the assumed values are given along with the observed values from the
present observations. "n" is the number of observations. The mean
differences for these observations from the assumed values are:
V = 0.000 +/- 0.003 (sigma), and b-y = -0.002 +/- 0.005 (sigma).
Table 1. Standard Star Observations
Star V (std) b-y V (obs) b-y n Remarks
HD 315 6.440 -0.078 6.444 -0.074 1 = 4 Cet = HR 11
HD 5319 8.046 0.601 8.042 0.601 3
HD 7615 6.693 0.025 6.687 0.025 1
BD-00 0288 8.831 0.710 8.832 0.709 1
HD161817 6.982 0.135 6.981 0.131 2
HD184914 8.178 0.799 8.176 0.795 1
BD-00 4073 9.905 0.779 9.907 0.779 2
HD200340 6.509 -0.031 6.510 -0.046 1 = HR 8054
HD209796 8.942 0.742 8.943 0.742 1
HD215141 9.239 0.962 9.238 0.960 2
HD217014 5.454 0.415 5.454 0.415 1 = 51 Peg = HR8729
HD218155 6.783 -0.004 6.784 -0.003 5
HD218918 5.163 0.076 5.163 0.076 1 = 59 Peg = HR8826
3. Discussion
The results for the comparison stars in the two fields are given in
Tables 2 and 3. Identification is made in the first column with the HD, BD,
or the Space Telescope Guide Star Catalogue (GSC). Colors for the stars in
the VZ Aqr field were measured on only one night, and so errors are not
listed. In general, expected errors are less than +/- 0.02 for stars brighter
than V mag. 11, rising to 0.06 for the faintest star in the HP And list.
The dwarf nova VZ Aqr and the bright star BD-03 5228 have been measured
by Echevarria et al. (1993) in the Stromgren four-color system; their V
and b-y are given in Table 2. Their observation of the bright star confirms
the present results within our mutual uncertainties. Remarkably, they have
also observed the dwarf nova declining from a 1986 outburst at nearly the
same brightness as I have.
In the HP And field, mention should be made of the very red star
GSC 2790-1851, which lies due south of the dwarf nova. The star's b-y
color corresponds to an approximate B-V near 2.3. (The star's color does
lie outside the range of the standards, but experience subsequent to the
present observations indicates the transformations are linear to at least
b-y = 1.8.) The star is not listed in the GCVS4 (Kholopov, et al. 1985) or
the NSV (Kholopov, et al. 1982) catalogues, nor does it appear in the
Stephenson (1989) catalogue of cool carbon stars. Nevertheless, such a star
is almost certainly variable in the few-tenths of a magnitude range, and
observers may wish to check on its brightness while viewing HP And. Even if
constant, the star will appear perhaps half a magnitude fainter visually than
indicated by the V magnitude here, since the effective wavelength of the
dark-adapted eye is somewhat bluer than the photometric V passband. Thus it
should be avoided as a comparison star for the dwarf nova.
Table 2. Photometry of Stars in the Region of VZ Aquarii
Star V b-y n Remarks
BD-03 5228 10.025 0.657 2 = GSC 5212-0590
.020 --
10.01 0.64 Echevarria et al.
GSC 5212-1650 12.315 0.449 2
.037 --
GSC 5212-0919 12.993 0.335 2
.019 --
GSC 5212-1612 12.961 0.017 1 = VZ Aqr, 1992 Aug 25.29 UT
12.80 0.04 1986 Jul 12, in decline, Echevarria et al.
Table 3. Photometry of Stars in the Region of HP Andromedae
Star V b-y n Remarks
HD 1469 9.240 -0.013 1 A0; = GSC 2790-1878
GSC 2790-1458 10.275 0.531 2
.014 .006
GSC 2790-0356 10.838 0.706 1
GSC 2790-1158 11.477 0.380 1
GSC 2790-1851 11.667 1.689 1 very red
GSC 2790-1757 11.741 0.632 1
GSC 2790-1885 14.032 0.303 1
Acknowledgement
Reduction and analysis of this data was facilitated by the use of the
SIMBAD database, operated by the Centre de Donnees astronomiques, Strasbourg,
France.
References
Echevarria, J., Costero, R., and Michel, R. 1993, Astr. & Astrophys. 275, 201.
Kholopov, P. N., et al. 1982, New Catalogue of Suspected Variables, Moscow.
Kholopov, P. N., et al. 1985, General Catalogue of Variable Stars, fourth
edition, Moscow.
Stephenson, C. B. 1989, A General Catalogue of Cool Galactic Carbon Stars,
second edition; Pubs. of the Warner & Swasey Observatory, vol. 3, no. 2.
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