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\IBVShead{5164}{4 September 2001}

\IBVStitle{USNO-A2.0 0825-15411768: A New Mira in Aquila}

\IBVSauth{Bedient, J. R.}

\IBVSinsto{1464 Molehu Dr.\ Honolulu, Hawaii 96818-1917 USA,
e-mail: {\tt bedient@hawaii.rr.com}}

%\SIMBADobj{USNO-A2.0 0825-15411768}
\SIMBADobjJ2000{IRAS 19179-0403}{19 20 35.029 -03 57 50.85}
\IBVStyp{  M  }

\IBVSabs{CCD observations of USNO-A2.0 0825-15411768 show it to vary on}
\IBVSabs{a 217.2-day period with an amplitude of about 2.2 magnitudes}
\IBVSabs{(broadband red).  It is classified as a Mira (M) variable.}

\begintext

The University of Illinois at Urbana-Champaigne's {\it Stardial\/}
instrument is an autonom\-ous drift-scan CCD camera mounted on the roof
of that institution's Astronomy building (McCullough and Thakkar
1997).  Consisting of a Kodak KAF400 CCD with a Nikon $f/1.4$ 50-mm focal
length 35-mm format camera lens stopped to $f/2.0$, the instrument records
nightly $8\times5$ degree images of a band of sky centered on $-4$ degrees
declination.  A broadband red-infrared filter (RG-1, passband 600 nm
and longer) is employed between the lens and the CCD\@.  A polynomial fit
to the background light of each image is subtracted, and the images are
immediately made available on the {\it Stardial\/} WWW site
(http://www.astro.uiuc.edu/stardial/) in both FITS and JPEG format.

While blinking {\it Stardial\/} images of an area in Aquila, a star
near R.A. 19\hr20\mm35\sec, Dec.\ $-03\deg57\arcm50\arcs$ (J2000) was
observed to vary in brightness.  A check of the GCVS (Kholopov et
al.\ 1998) revealed no known variable star at or near that position,
however the TASS tenxcat (Richmond et al.\ 2000) contained a series of
Johnson $V$-band observations associated with the star GSC 5138-0446
(USNO magnitudes $m_B=13.1$, $m_R=11.6$, position R.A.
19\hr20\mm36\fsec51, Decl.\ $-03\deg58\arcm18\farcs9$, J2000 from
GSC-ACT via Visier) that showed variability between magnitude 11.4 and
12.0.  Viewing the area using the {\it Aladin\/} interactive sky atlas
revealed another TASS detection (TASS J192035.3-035756) quite near the
first -- and the two sources appeared to vary in phase with each
other.  The second source was apparently associated with another red
star, USNO-A2.0 0825-15411768 (USNO2 magnitudes $m_B=14.9$, $m_R=11.9$,
J2000 position R.A. 19\hr20\mm35\fsec029,
Dec.\ $-03\deg57\arcm50\farcs85$).  Which star was the variable?

The TASS Mark III cameras have 13.4 arcseconds/pixel resolution, and the
FWHM of stellar images range from 2.5 to 4.0 pixels.  The GSC star and
the USNO star are separated by 36 arcseconds.  Therefore, the two stars
were frequently merged. 

The necessary confirmation was found on Digitized Sky Survey\\
(http://archive.stsci.edu/dss/) images of the area.  First and second
generation red images of the area are presented in Figure~1.  Comparing
the two images, taken nearly 4 years apart, USNO-A2.0 0825-15411768
(indicated by tick marks in the left-hand, first generation image) is
clearly the variable.  For field identification, three prominent stars
are identified on the right-hand, second generation image.

\IBVSfig{8cm}{5164-f1.eps}{Comparison of Digital Sky Survey red plates of
USNO-A2.0 0825-15411768.  Tick marks on the left image indicate the
variable.  Three field stars are identified on the right image: A = GSC
5138-0815, B = GSC 5138-0058, C = GSC 5138-0446}

\vskip-11pt
With the variable identified, all available {\it Stardial\/} images of
the region were analyzed.  293 images covering portions of six
observing seasons 1996--2001 were found suitable for differential
photometry.  A comparison star, SAO 143290, and a check star, SAO
143252, were chosen, and differential magnitudes were extracted from
each image.  As the {\it Stardial\/} images have a scale of approximately
35 arcseconds per pixel, over double that of the TASS Mark III cameras,
the variable and GSC 5138-0446 are certainly merged in {\it Stardial\/}
images.  The contribution of GSC 5138-0446 to the total light of the
pair, calculated from its red plate magnitude of 11.6, was subtracted
from each observation. The results, along with 26 TASS $I$-band
observations (converted to differential magnitudes) that are
unambiguously associated with USNO-A2.0 0825-15411768 are plotted in
Figure~2 and given in the electronic table 5164-t1.txt.

\IBVSedata{5164-t1.txt}

\IBVSfig{8cm}{5164-f2.eps}{Light Curve of USNO-A2.0 0825-15411768.  Filled
diamonds represent the variable, open triangles are TASS Mark III
$I$-band data, open circles represent the check star, and the dashed
curve is computed from elements given in the text}

\vskip-11pt
Regular variations of about 2.2 magnitudes in amplitude are seen.  At
first glance, the low amplitude would seem to be cause to classify this
star as SRa; however the combination of the KAF400 CCD and RG-1 filter
minimizes the effect of ``amplitude excess'' caused by TiO absorption
bands (Celis 1978).  Though we lack unambiguous 
$V$-band data, the visual
amplitude is probably at least 3 magnitudes.  TASS data show that $V-I$
near maximum light is 3.6 magnitudes, indicating a spectral type of
M4-5 and an effective temperature of 3000 K (Zombeck 1990).  The star
is therefore classified as a Mira-type variable.

Infrared data from the IRAS Point Source Catalog support a conclusion
that this star is likely a mass-losing AGB variable.  USNO-A2.0
0825-15411768 is located within the uncertainty ellipse of IRAS
19179-0403.  The star's average $I$-band flux, calculated from TASS
data,  when compared to the IRAS 12 and 25 micron infrared fluxes
(Table 1) demonstrate an infrared excess consistent with a
circumstellar dust shell as observed in other stars of this type
(Little-Marenin and Little 1997).

\begin{table}[t]
\caption{Infrared fluxes for USNO-A2.0 0825-15411768}
\begin{center}
\begin{tabular}{cc}
\hline
$\lambda$ (microns) & Flux (Jy) \\
\hline
0.79 & 1.71 \\
12 & 1.63 $\pm$0.1 \\
25 & 0.698 $\pm$0.01 \\
\hline
\end{tabular}
\end{center}
\end{table}

Three maxima, at JD 2,450,325; 2,450,970 and 2,451,412 are well
observed.  A simple graphical solution (Richter et al.\ 1985, p.\ 16)
yielded a best-fit period of 217.2 days.  With only three maxima to
work from, this period must be regarded as preliminary in nature.
Initial elements for USNO-A2.0 0825-15411768 are thus:
$$ {\rm JD_{max}} = 2450323.4 + 217.2 \times E. $$
The above elements may be affected slightly by infrared phase lag due
to the combination of filter and CCD used.  Maximum light of Miras in
the infrared typically occurs near visual phase 0.1 to 0.2 (Pettit and
Nicholson 1933; Lockwood and Wing 1971).

Acknowledgements:

My sincere thanks go to James Bauer of the University of Hawaii
Institute for Astronomy for assistance in interpreting IRAS data; and
Dr. Michael Richmond, Dept. of Physics, Rochester Institute of
Technology, for providing information on TASS Mark III cameras and
assistance in interpreting TASS data.

This research has made use of the VizieR catalogue access tool and the
Aladin interactive sky atlas, CDS, Strasbourg, France, and NASA's
Astrophysics Data System Bibliographic Services.

The Second Palomar Observatory Sky Survey (POSS-II) was made by the
California Institute of Technology with funds from the National Science
Foundation, the National Aeronautics and Space Administration, the
National Geographic Society, the Sloan Foundation, the Samuel Oschin
Foundation, and the Eastman Kodak Corporation. The Oschin Schmidt
Telescope is operated by the California Institute of Technology and
Palomar Observatory.

\clearpage

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\endreferences

\end{document}

