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\IBVShead{5778}{19 June 2007}

\IBVStitle{H{\boldmath $\alpha$} Observations of the Binary System HR 2142}

\IBVSauth{Pollmann, E.}

\IBVSinsto{Email: ErnstPollmann@aol.com}

\SIMBADobjAlias{HR 2142}{HD 41335}

\begintext

HR 2142 (HD 41335, V696 Mon) is a Be star of visual magnitude 5.2 mag. In
the past 50 years it was the subject of many studies. Its projected
rotational velocity ($v \sin i$) is very high (350--400 km/s) (Peters, 1972;
Slettebak, 1982).  The extreme width of the emission lines made it
difficult to classify the spectrum, but today HR 2142 is classified as
B2IVe. The most remarkable characteristics of its spectrum are the Balmer
emission lines with a central reversal or absorption feature from the
circumstellar envelope. Since the discovery of periodic profile variations
in the Balmer lines HR 2142 has been considered to be a binary system with an
orbital period of 80.86 days (Peters, 1983, 2001; Peters \& Gies,
2002). The circular orbital solution was obtained from RV measurements
based upon measurements of the wings of the broad Balmer and He lines
(Peters, 1983). The ephemeris from that paper:
 $$
 T = {\rm JD~} 2441990.5 \pm 1.1,\qquad
 P = 80.860 \pm 0.005~{\rm days}
 $$ 
 was used for calculation of the phases here. The periodic behaviour
mainly pertains the appearance of primary and secondary shell
phases (Peters, 1972). This is indicated by the appearance of shell
(absorption) lines in the emission Balmer profiles and by periodic H$\alpha$
$V/R$ variations.

Since the azimuthal distribution of this plasma material is complex and
the H$\alpha$ profile comes from extended disk regions, a tomographic
study for mapping the $V/R$-variations is considered particularly useful.
It may contribute to clarify whether the variability is further strictly
periodic or whether there are references of disturbances by disk
instability (completely without companions) or tidal disturbances.
Therefore Monika Maintz and Thomas Rivinius, then staff astronomers from
the Landessternwarte Heidelberg in Germany, suggested a collaboration with
amateur astronomers who could provide line profile observations with a
more frequent coverage than it is possible at large observatories. In
general the strength of central reversal depends on the inclination of the
binary'’s orbital plane to the line of sight. High inclination causes a
strong central absorption, because the infalling gas intersects the line
of sight. With a dispersion of at least 35 \AA{}/mm and $R \sim 12000$
these $V/R$ variations can be observed with instruments now available to
amateurs.

The spectra discussed here were obtained with a 20-cm ($f/4$)
Schmidt--Cassegrain telescope at the observatory of the Vereinigung der
Sternfreunde, K\"oln, connected with a slitless spectrograph: dispersion =
27 \AA{}/mm, $R\sim 14000$. Fig.~1 illustrates my findings with 30
individual H$\alpha$ spectra that were obtained from September 2003 to
April 2006.

\IBVSfigNoCaption{11cm}{5778-f1a.ps}
 \IBVSfigKey{5778-f1a.ps}{HR 2142}{H alpha profile}

\vspace{-24pt}

\IBVSfigNoCaption{11cm}{5778-f1b.ps}
 \IBVSfigKey{5778-f1b.ps}{HR 2142}{H alpha profile}

\newpage

\IBVSfig{11cm}{5778-f1c.ps}{{\hspace{-4pt}\bf a--c.} The three panels show
the H$\alpha$ profiles arranged according to the orbital phase. It can be
seen that the $V/R$ ratios during the orbital period are mostly less than
1, while between phases 0.75 and 0.07 the $V/R$ ratios larger than 1
are more common. During the shell phase the absorption component in
H$\alpha$ is flanked by the emission. On the other hand, we do not see any
strict periodic behaviour of the $V/R$ ratio like in some (but not all)
other binary systems. This fact can be an indication of a complicated
behaviour in the circumstellar matter in the system of HR 2142}
 \IBVSfigKey{5778-f1c.ps}{HR 2142}{H alpha profile}

Depending on the orbital phase, we see the enhanced emission either red-
or blueshifted as $V/R$ variation. The central reversal develops around
phase 0.0 or 1.0, when an additional plasma material infall is in front of
the Be primary. At this phase the companion is between the observer and
the Be star. The extent, to which the disk is symmetrically distributed
with respect to the line of sight, affects the observed strength of the
$V$ and $R$ peaks.

Within the three observational periods different orbits are phasedly
represented. Fig.~1 shows variations with the orbital phase and some
changes from cycle to cycle. The legend at right identifies the orbital
phase of each spectrum. The phase-dependent $V/R$ behavior derived from
these spectra is shown in Fig.~2.

The uncertainties on EW and $V/R$ were determined by measurements of
standard stars on three nights for a total of 8 hours of observation. For
both values uncertainty was less than 3\% for individual measurements at
one night. A sharp decrease in $V/R$ between phases 0.9--1.04 is clearly
visible. The derived $V/R$ ratios of the spectra between 09/2003--–04/2006 
have maximum values of 1.07 at phase 0.85 (2003/2004), 1.22 at phase 0.93
(2004/2005) and 1.16 at phase 0.9 (2005/2006). In addition there is a
remarkable $V/R$ change between phases 0.5 and 0.6. At these phases, the
companion is behind the primary component. The $V/R$ change is also
observable here, similar to the situation at phase 1.0, although it is
less pronounced because of the eclipse of the primary.

\IBVSfig{8cm}{5778-f2.ps}{$V/R$ variation of H$\alpha$ based on observations from
09/2003--04/2004, 09/2004--01/2005, 10/2005--04/2006}
 \IBVSfigKey{5778-f2.ps}{HR 2142}{V/R variation}


{\bf Acknowledgment.} The author thanks Dr.~Monika Maintz and Dr.~Thomas
Rivinius (both formerly from Landessternwarte Heidelberg) for encouraging
this study, and Dr.~Reinhard Hanuschik (European Southern Observatory) and
Dr.~Anatoly Miroshnichenko (University of North Carolina at Greensboro)  
for carefully reading the manuscript.

\references

Peters, G.J., 1972, {\it PASP}, {\bf  84}, 334

Peters, G.J., 1983, {\it PASP}, {\bf  95}, 311

Peters, G.J., 2001, {\it Publications of the Astron. Inst. Acad. Sci. Czech Republ.}, {\bf 89}, 30
%Original: Pub. .... {\bf 89}, 29
%Corrected: Thu Jun 21 11:15:27 MEST 2007

Peters, G.J., Gies, D.R., 2002, {\it ASP Conference Series}, {\bf 279}, 149, in:  Exotic
Stars as Challenges to Evolution, ed.\ Christopher A. Tout \& Walter Van Hamme, ASP, San
Francisco (= {\it Proc.\ IAU Coll.}, {\bf 187}, 149)

Slettebak, A., 1982, {\it ApJS}, {\bf  50}, 55

\endreferences

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