\documentstyle[twoside, epsf]{article}

\input ibvs2.sty

\begin{document}

\IBVShead{4564}{6 March 1998}


\IBVStitle{The radial velocity of the \lowercase{ro}A\lowercase{p} star $\gamma$\,E\lowercase{qu}}

\IBVSauth{D.E.~MKRTICHIAN$^1$, N.N.~SAMUS$^2$, N.A.~GORYNYA$^2$, S.V.~ANTIPIN$^3$, P.~NORTH$^4$,\\~~~~A.S.~RASTORGOUEV$^3$, E.V.~GLUSHKOVA$^3$, M.G.~SMEKHOV$^3$, M.E.~SACHKOV$^2$}

\IBVSinst{Astronomical Observatory, Odessa State University, Shevchenko Park, Odessa, 270014, Ukraine}
\IBVSinst{Institut  of Astronomy, Russian Academy  of Sciences, Pyatnitskaya Str. 48, Moscow 109017, Russia}
\IBVSinst{Sternberg State Astronomical Institute, Universitetsky prospect 13, Moscow, 119899, Russia}
\IBVSinst{Institut d'Astronomie de l'Universite de Lausanne, CH-1290 Chavannes-des-Bois, Switzerland}

\SIMBADobj{gamma Equ}
\IBVStyp{ Ap }
\IBVSkey{radial velocities}

\begintext
\bigskip

The sharp-line cool magnetic SrCrEu star $\gamma$\,Equ (HD\,201601) is
a very slowly rotating star (P\,$\simeq$\,74 years, Leroy et al., 1994)
and is well known as a roAp star with at least four excited
unstable modes (Martinez et al., 1996). The radial velocities  obtained
during the history of investigations of this star did not show any
long-term variations larger than the observational errors. Recently,
Scholz et al. (1997) published their results of radial velocity
measurements of $\gamma$\,Equ made in 1995 and 1996. Nine of their
radial velocities show a rapid increase from a mean value of
$-16.81$~km\,s$^{-1}$ up to a maximum at $-4.28$~km\,s$^{-1}$ within
the interval JD\,2449608 - JD\,2450356, while two later measurements
(on JD\,2450391 and JD\,2450410) show a decreasing $V_r$ which seems
to converge towards previous values. They suggested that $\gamma$\,Equ
is a long-period binary star with a high eccentricity.

The results of Scholz et al. (1997, hereafter S97) disagree with our
758 homogeneous radial velocity estimations for $\gamma$\,Equ
collected using a cross-correlation technique, during 27 nights in
1994, 1995 and 1996. The epochs of our measurements encompass the
phase of the magnetic minimum and many of the nights on which S97
observed, including a most critical one.

The main part of our observations were carried out within a collaboration
between Odessa Observatory (Ukraine) and Institute of Astronomy,
Russian Academy Sciences (Russia) on radial velocity investigations of
selected chemically peculiar stars (Mkrtichian et al. 1997).
We have used the 1.0m and 0.6m telescopes of Simeiz Observatory (Mt. Koshka,
Crimea, Ukraine) and the 0.7m telescope of Sternberg Institute (Moscow, Russia)
equipped with the transportable CORAVEL-type scanner (hereafter RVS),
 (Tokovinin 1987).
Brief reports on rapid photometric and radial-velocity variations
of the roAp star $\gamma$\,Equ will be given in two papers by Mkrtichian (1998) and
Mkrtichian et al. (1998), while the present publication is devoted to
the long-term behaviour of the radial velocity of $\gamma$\,Equ. Two
radial velocity measurements -- one of which at a most critical
date -- were also acquired at Observatoire de Haute-Provence (CNRS,
France), using the 1.0m Swiss telescope equipped with the CORAVEL
scanner (Baranne et al. 1979), as part of a programme of search for
binaries among cool Ap stars.

The observational procedure on RVS and CORAVEL scanners includes blocks of
measurements of the star, immediately preceded and followed by a velocity
calibration exposure using an internal Ne discharge lamp (RVS) or a Fe hollow
cathode lamp (CORAVEL). During every night, several measurements of
radial-velocity standard stars were used for correction of low amplitude
instrumental drifts.

In Table 1, the journal of radial velocity observations is presented.
\vskip 1cm
\centerline{Table 1. The journal of 1994 - 1996 radial velocity observations
of $\gamma$\,Equ.}
\vskip 3mm
\begin{center}
\begin{tabular}{|ccccccc|}
\hline
$HJD_{start}-HJD_{end}$&Mean $V_{r}$&Error&N&Tel.&Observatory&Observer(s)\\
&km\,s$^{-1}$&$\pm$km\,s$^{-1}$&&m&&\\
\hline
  2449530.536 - .556&$-$17.00 &0.144 &17   &1.0&SO&RAS\\
  2449556.540 - .549&$-$16.03 &0.302 &8    &1.0&SO&SNN\\
  2449569.424 - .437&$-$17.13 &0.094 &8    &0.6&SO&SNN\&GNA\\
  2449607.393 - .407&$-$16.61 &0.289 &11   &0.6&SO&SMG\&SME\\
  2449608.300 - .351&$-$17.08 &0.216 &24   &0.6&SO&SMG\&SME\\
  2449609.425 - .439&$-$17.38 &0.220 &11   &0.6&SO&SMG\&SME\\
  2449636.170 - .259&$-$15.350&0.131 &44   &0.7&SAI&SNN\\
  2449648.195 - .284&$-$19.816&0.068 &49   &0.7&SAI&SNN\\
2450042.261  &$-$16.86 &0.46  &1    &1.0&HP&MJC\\
2450254.5347 - .5416&$-$16.91 &0.135 &11   &1.0&SO&RAS\\
2450255.5216 - .5355&$-$16.40 &0.149 &19   &1.0&SO&RAS\\
2450256.5265 - .5397&$-$16.39 &0.285 &18   &1.0&SO&RAS\\
2450257.5273 - .5432&$-$16.74 &0.224 &22   &1.0&SO&RAS\\
2450258.5280 - .5405&$-$16.70 &0.179 &17   &1.0&SO&RAS\\
2450264.5472 - .5604&$-$17.05 &0.145 &18   &0.6&SO&RAS\\
2450265.5479 - .5618&$-$17.07 &0.110 &19   &0.6&SO&RAS\\
2450267.5501 - .5647&$-$16.83 &0.303 &18   &1.0&SO&GEV\\
2450268.558 - .567 &$-$16.97 &0.293 &13    &1.0&SO&GEV\\
2450269.551 - .559 &$-$16.97 &0.246 &11   &1.0&SO&GEV\\
2450270.549 - .556 &$-$16.64 &0.308 &10   &1.0&SO&GEV\\
2450271.554 - .559 &$-$16.17 &0.463 &8    &1.0&SO&GEV\\
2450272.5592 - .5636&$-$16.89 &0.304 &10   &1.0&SO&GEV\\
2450285.4864 - .4954&$-$18.15 &0.168 &11   &0.6&SO&SME\\
2450316.4801 - .5783&$-$16.69 &0.054 &115  &0.6&SO&AS\&MDE\\
2450319.3284 - .4489&$-$16.60 &0.049 &126  &0.6&SO&AS\&MDE\\
2450321.3158 - .4652&$-$16.86 &0.055 &137  &0.6&SO&AS\&MDE\\
2450355.384         &$-$16.77 &0.45  &1  &1.0&HP&vES\\
\hline
\end{tabular}
\end{center}
{\bf Observatory:}\\ SO - Simeiz Obs.,  SAI - Sternberg Astron. Inst.,
HP - Haute-Provence Observatory.\\
{\bf Observer(s):}\\
 ASV --- S.V. Antipin, GEV --- E.V. Glushkova, GNA ---
N.A. Gorynya,
MDE --- D.E. Mkrtichian, MJC --- J.-C. Mermilliod, RAS --- A.S. Rastorgouev,
 SNN --- N.N. Samus, SME --- M.E. Sachkov, SMG --- M.G. Smekhov, vES
 --- S. van Eck.

\eject

\IBVSfig{10cm}{4564-f1.ps}{The 1994-1996 radial velocities of $\gamma$\,Equ: full dots --- RVS data, triangles --- CORAVEL data, crosses --- Scholz et al. (1997) data}
\vskip 3mm

Figure 1 shows the mean radial velocities of $\gamma$\,Equ versus the Julian
Date in 1994--1996, obtained with RVS (full dots), CORAVEL (triangles),
and by S97 (crosses).
 As can be seen, our numerous cross-correlation radial
velocities (758 estimations) cover the 1994--1996 interval,
but do not show any drastic increase during the year 1996, contrary to
what S97 reported. For instance, our radial velocity estimate of
$-16.77$ at the epoch HJD\,2450355.384 was obtained just one hour
before the measurement yielding $Vr = - 5.28$~km\,s$^{-1}$ according
to S97 (at HJD 2450355.426), which makes a difference as large as
$-11.49$~km\,s$^{-1}$. Whereas our results are in full agreement, not
only with our own previous values, but also with all radial velocities
published in the literature, those published by S97 are clearly
discrepant. Our data show that the radial velocity of $\gamma$\,Equ
has remained constant within the errors on long timescales at a value
which, during the 1994-1996 interval, amounted to
$-16.83\pm0.038$~km\,s$^{-1}$.

We can summarize the results of our note as follows:

\begin{itemize}
\item  We obtained 758 new, homogeneous and precise radial velocities of
$\gamma$\, Equ in 1994--1996 using cross-correlation scanners.
\item  The mean radial velocities for individual nights of 1994--1996 are
constant on long timescales within the errors and average to
$-$16.83$\pm$0.038 km\,s$^{-1}$. This value is close to the average
radial velocity for the last 70 years.
\item Our numerous radial-velocity measurements of $\gamma$\,Equ, the
epochs of which largely overlap those of S97, do not show any significant
increase of radial velocity at the time of the year 1996 when such a change
occurred according to S97. We conclude that there is as yet no evidence for
a binary companion to $\gamma$\,Equ.
\end{itemize}



\references

Baranne A., Mayor M., Poncet J.L., 1979, {\it Vistas in Astronomy}, {\bf 23}, 279


Leroy J.L., Bagnulo S., Landolfi M., Landi Degl'Innocenti E., 1994,
 {\it A\&A}, {\bf 284}, 174

Martinez P., Weiss W.W., Nelson M.J., Kreidl T.J., Roberts G.R.,
Mkrtichian D.E., Dorokhov N.I., Dorokhova T.N., Birch P.V., 1996,
 {\it MNRAS}, {\bf 282}, 243

Mkrtichian D.E., Samus N.N., Gorynya N.A., 1997, {\it in: Stellar Magnetic Fields,
eds. Yu.V. Glagolevskij and I.I. Romanyuk, Moscow}, 185

Mkrtichian D.E., 1998, {\it IBVS} (submitted)

Mkrtichian D.E., Samus N.N.,  Gorynya N.A., Antipin S.V., 1998,
(in preparation)

Scholz G., Hildebrandt G., Lehmann H., Glagolevskij Yu.V., 1997, {\it
A\&A}, {\bf 325}, 529

Tokovinin A.A., 1987, {\it Soviet Astronomy}, {\bf 31}, 98


\end{document}



