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\IBVShead{5528}{18 May 2004}

\IBVStitle{First Spectrum of NSV\,19451 -- the Wrong Star?} 

\IBVSauth{Schmidtobreick, L.$^1$; Tappert, C.$^2$}

\IBVSinst{European Southern Observatory, Casilla 19001, Santiago 19, Chile}
\IBVSinst{Departamento de Astronom\'{\i}a y Astrof\'{\i}sica, 
          Pontificia Universidad Cat\'olica, Casilla 306, Santiago 22, Chile}

\SIMBADobj{NSV 19451}
\IBVStyp{  NL  }
\IBVSkey{stars: spectroscopy - stars: variables: cataclysmic variables}

\IBVSabs{We present optical spectroscopy}
\IBVSabs{of the suspected cataclysmic variable NSV 19451.}
\IBVSabs{The spectrum demonstrates it to be a late G type main sequence star} 
\IBVSabs{and thus indicates that the object has been either misclassified}
\IBVSabs{or misidentified.}

\begintext

\vspace*{-1cm}

The star NSV\,19451 has been found to be variable by Kolrvatykh (1983)
while observing stars in the Hydra--Centaurus region and especially 
the Mira Cet type variable EW\,Hya. 
He found that 
EW\,Hya did not show high enough variations ($14\mm - 16\mm$ pg,
$P = 250\day$), and thus considered its classification doubtful.
Instead, in its vicinity, he found the variable star who later got the 
designation NSV\,19451. This star varied around 1\,mag
between $V = 16\fmm2$ and $17\mm$ and is as such listed in 
the catalogue by Kazarovets et al. (1998) with the probable classification
as a cataclysmic variable of U Gem subtype. It has thus been 
included into the atlas of 
Downes et al. (2001) who also provide a finding chart of the object.

Recently, NSV\,19451 has been observed by Berto Monard (vsnet--alert 8120)
who also listed the occurrences of the object in various catalogues. 
Taking also these listed values into account, he 
found the object to be a `reasonably constant white--blue
star around $V = 14\fmm4$'. He suspected the object to show
emission lines indicating the cataclysmic variable nature, and 
concluded that the
quoted magnitude range in the atlas of Downes et al. (2001) seems to be 
incorrect. Note that the atlas, as living edition, has been updated immediately 
and the magnitude range now includes Monards measurements as well.

To check the classification of NSV\,19451 as cataclysmic variable and especially
as U\,Gem type star, we 
performed spectroscopic observations using the  
ESO Faint Object Spectrograph and Camera (EFOSC2) at the 3.6\,m telescope
on la Silla, Chile. Two spectra, each of 10\,min exposure time, have been 
obtained on 2004-05-01 at UT 02:25 using
grism \#6 and a $1\arcs$ slit. 

Standard reduction has been performed with IRAF.
The BIAS has been subtracted and the data have been divided by a flat field,
which was normalised by fitting Chebyshev functions of high order 
to remove the detector specific spectral response. 
The two spectra have been combined and then optimally extracted (Horne, 1986).
Wavelength calibration yielded a final FWHM resolution
1.2\,nm and a spectral range of 390\,nm to 790\,nm.
The spectrum has been corrected for the instrument function
and was flux--calibrated using the spectrophotometric standard LTT\,3218.
However, as the night was not of photometric condition, 
the absolute flux--values have to be regarded with caution.

\IBVSfig{9cm}{5528-f1.eps}{The optical spectrum of NSV\,19451 (upper plot) 
and the
best fitting template spectrum, a G6--8 type main sequence star
(Silva \& Cornell, 1992). Scaled to the same average flux value
and arbitrary shifted down for purpose of clarity.\label{hyas}}
\IBVSfigKey{5528-f1.eps}{NSV 19451}{spectrum}

\vspace*{-0.4cm}

The resulting spectrum is plotted in Fig. \ref{hyas}. It is 
dominated by absorption lines, mainly the Balmer series, Ca\,I and II, Na\,I, 
and the strong G--band at 430\,nm. We have used the catalogues of Pickles (1985)
and Silva \& Cornell (1992) for classification and find the object to match
a medium/late G--type dwarf. The best fitting template spectrum, of 
G6--8V type by Silva \& Cornell has been over--plotted for comparison.
We have found no signal of any emission lines or any other spectral
feature which might indicate that NSV\,19451 is a cataclysmic variable. 
Instead, it seems to be
a perfectly normal G--type star and most probably is not variable at all.

This conclusion is in perfect agreement with the findings of Monard
that NSV\,19451 does not show any light variations. However, Kolrvatykh
(1983) observed its variability. So either, the object has been variable
in the past but is behaving like a constant G--type star now, or the
variable star observed by Kolrvatykh and listed as NSV\,19451 by 
Kazarovets et al (1998) 
and the G--type star which is believed to be
NSV\,19451 are not the same object.

We rather believe the latter conclusion to be the case. For once, there is
no variable type known which in outburst ($V=14\mm$ now instead of 
16--17$\mm$ before) resembles a G--type dwarf. On the other hand, the
finding chart given by Downes et al. (2001) is done via coordinate match
only and there are several fainter stars in the vicinity of the
labelled object who might be the real candidate for Kolrvatykh's variable star.
In fact, as Kolrvatykh does not give any coordinates nor uncertainties
of the star he has observed but just states that it is in the vicinity of
EW\,Hya, it is rather difficult to judge the ambiguity in the finding chart.

Time resolved photometry on all stars in the vicinity of the proposed position
should help to clarify this issue and to recover the true variable NSV\,19451
and maybe even the ambiguous Mira--star EW\,Hya.

\bigskip

{\bf Acknowledgement:} We are grateful to Valentin Ivanov for his translation 
of Kolrvatykh's publication from Russian.

\newpage

\references

Downes, R.A., Webbink, R.F., Shara, M.M., Ritter, H., Kolb, U., Duerbeck, H.W., 2001, 
{\it PASP}, {\bf 113}, 764, living edition. 
%%\BIBCODE{2001PASP..113..764D} 

Horne, K., 1986, {\it PASP}, {\bf 98}, 609
%%\BIBCODE{1986PASP...98..609H}

Kazarovets, E.V., Durlevich, O.V., Samus, N.N., 1998, {\it IBVS}, {\bf 4655}
%%\BIBCODE{1998IBVS.4655....1K}

Kolrvatykh, E.N., 1983, {\it ATsir}, {\bf 1252}, 4 
%%\BIBCODE{1983ATsir1252....4K}

Pickles, A.J., 1985,  {\it ApJ Suppl.}, {\bf 59}, 33
%%\BIBCODE{1985ApJS...59...33P} 

Silva, D.R., Cornell, M.E., 1992, {\it ApJ Suppl.}, {\bf 81}, 865
%%\BIBCODE{1992ApJS...81..865S}

\endreferences


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