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\IBVShead{5440}{10 July 2003}

\IBVStitle{H\boldmath{$\alpha$} variations of the spotted G dwarf AP 149}

\IBVSauth{Savanov, I.$^1$; Strassmeier, K.$^1$;  Romanyuk, I.$^2$; Kudryavtsev, D.$^2$}

\IBVSinst{Astrophysical Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany; e-mail: isavanov@aip.de, kstrassmeier@aip.de}

\IBVSinst{Special Astrophysical Observatory RAS, Nizhnij Arkhyz, Zelenchukskaya, Karachai-Circassian Republic, 369167, Russia; e-mail: roman.@sao.ru, dkudr@sao.ru }

\IBVSobj{AP 149}
\IBVSabs{High resolution spectroscopic observations of G dwarf AP 149}
\IBVSabs{in the alpha Persei cluster result in the estimations of}
\IBVSabs{variations of the equivalent widths and fluxes radiated in H-alpha}
\IBVSabs{line.}


\begintext

AP 149  is a rapidly rotating G dwarf with a rotation period of
0.32 days, $v\sin i$ of 102~km\,s$^{-1}$ and an inclination of
30\deg (Barnes et al., 2001). It belongs to the $\alpha$
Persei cluster at a distance of 180--187 pc and an age of about
50~Myr. Barnes et al. (1998, 2001) and Jeffers et al. (2002) used
the advantages of a multi-line cross-correlation technique to gain
S/N in order to perform Doppler imaging of several $\alpha$ Persei
cluster G dwarfs. Their image reconstructions demonstrated that
these stars have high latitude and/or polar spots and low latitude
features. The original aim of our work was to extend the work by
Barnes et al. (1998, 2001) by studying the starspot distribution
on a few $\alpha$ Persei cluster stars several yeas after their
initial observation. In this paper, we present some first science
verification data.

Spectroscopic observations of  AP 149  were to be obtained with the 6m
telescope of the SAO RAS on the nights of October 22 and 23, 2002.
The 2K$\times$1K CCD camera was used with the main stellar
spectrograph in the Nasmyth focus. With an entrance slit of
1\arcs, the spectral resolution was R=24,000. The spectral region
from 6200 \AA~ to 6610 \AA~ was selected. It includes the
6400~\AA~-- 6440~\AA~ region often used for Doppler imaging as
well as H$\alpha$ at 6563~\AA~ for the search for variations of
its profile.

We intended to obtain full phase coverage for AP 149 during these
two consecutive nights. Unfortunately, due to the weather
conditions only 3 spectra of 30 min exposures each were obtained
on October, 23. The heliocentric Julian Dates of the exposures are
2,452,571.2792, 2,452,571.3160,  and 2,452,571.3417. They were
supplemented by calibration spectra including Th-Ar, flat field,
and bias, and two spectra of the comparison star HD~10780 (K0V).
%Observations are separated by 0.0, 0.115 and 0.195 of 0.320 days period.
Data reduction was done at SAO with the MIDAS package. S/N ratio
for the spectra of AP 149 is about 30-40. A fragment of the
spectra of AP 149, as well as  HD~10780, is shown in the left part
of Fig.~1.

The most prominent spectral feature is the H$\alpha$ emission
line (Fig.~1). The range of variability in the emission line
profiles can be estimated from the plot in the lower right panel
of Fig.~1. A double-peaked profile is evident at the phases of our
observations but, after the subtraction of the theoretical
hydrogen line profile convolved with the appropriate rotational
profile for AP 149 of 102 km s$^{-1}$ (Barnes et al., 2001), the
H$\alpha$ profiles exhibit a triangular shape with additional
features possibly connected with transients (Barnes et al., 2001).
Synthetic spectra were calculated with the atmospheric parameters
$T_{\rm eff}$=5500~K and $\log g$=4.0 from the Kurucz (1993) grid
of models with solar metalicity.

The equivalent width of the H$\alpha$ emissions is 4.2, 4.6 and
4.9 ~\AA\ from the 3 spectra, respectively, with errors less, than 0.1 \AA , thus we observed a real increase. Under the assumption
of V=11\fmm71 (Barnes et al., 2001) the flux radiated in
H$\alpha$ is in the range of (0.26~--~0.31) 10$^{-12}$
erg\,cm$^{-2}$s$^{-1}$\AA$^{-1}$.

\IBVSTack{This research has made use of DFG grant STR645/1-1.}

\IBVSfig{12cm}{5440-f1.eps}{Left column: High-resolution spectra of AP 149 
(top) and, for comparison, HD~10780 (bottom, shifted) in three
wavelength ranges. Right column: Top: Residual H$\alpha$ line
profiles after subtraction of a synthetic spectrum for our 3
observation (profiles were arbitrarily shifted). Bottom:
H$\alpha$ profiles of AP 149 compared to the unbroadened
synthetic spectrum (shifted by $-$0.1) and its broadened version.
}
%%\IBVSfigKey{5440-f1.eps}{AP 149}{spectra}

\references

Barnes, J.R., Collier Cameron, A., Unruh, Y.C., et al.,
1998, MNRAS, {\bf 299}, 904

Barnes, J.R., Collier Cameron, A., James, D.J, Steeghs, D.I.,
2001, MNRAS, {\bf 326}, 1057


Jeffers, S.V., Barnes, J.R., Collier Cameron, A., 2002, MNRAS,
{\bf 331}, 666

Kurucz, R. L., 1993, ATLAS-9, CD-ROM \# 13


\endreferences

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