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\input ibvs2.sty

\begin{document}


\IBVShead{6060}{14 June 2013}

\IBVStitletl{Photometric and spectroscopic variations}{ of the B\lowercase{e} star HD\,112999{\IBVSfm }}

\IBVSauth{\noindent Corti, M. A.$^{1,2}$; Gamen, R. C.$^{2,3}$; Aidelman, Y. J.$^{2,3}$; Ferrero, G. A.$^{2,3}$; Weidmann,~W.~A.$^{4}$}


\IBVSinst{Instituto Argentino de Radioastronom\'{\i}a (CCT-La Plata, CONICET),Villa Elisa, Argentina}
\IBVSinst{Facultad de Ciencias Astron\'omicas y Geof\'{\i}sicas, Universidad Nacional de La Plata, Argentina \\
\indent e-mail: {mariela@fcaglp.unlp.edu.ar}}
\IBVSinst{Instituto de Astrof\'{\i}sica de La Plata (CCT-La Plata, CONICET), Argentina}
\IBVSinst{Observatorio Astron\'omico C\'ordoba, Universidad Nacional de C\'ordoba, Argentina}


\SIMBADobj{HD 112999}
\IBVStyp{  Be star  }
\IBVSkey{Stars: emission-line, Be - Stars: individual: HD 112999 - Stars: variables:}
\IBVSabs{general Be objects are stars of B spectral type showing lines of the Balmer }
\IBVSabs{series in emission. The presence of these lines is attributed to the existence} 
\IBVSabs{ of an extended envelope, disk type, around them. Some stars are observed in } 
\IBVSabs{both the Be and normal B-type spectroscopic states and they are known as }
\IBVSabs{transient Be stars. In this paper we show the analysis carried out on a new}
\IBVSabs{possible transient Be star, labelled HD 112999, using spectroscopic optical}
\IBVSabs{observations  and  photometric data.}

\begintext

\section{Introduction}

{\IBVSfoot{Visiting Astronomer, Complejo Astron\'omico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Cient\'{\i}ficas y T\'ecnicas de la Rep\'ublica Argentina and the National Universities of La Plata, C\'ordoba and San Juan.} }

Be stars were defined as ``non-supergiant B-type stars whose spectrum have or had at a time, one or more Balmer lines in emission"  by Jaschek et al. (1981).
This class of stars has circumstellar disks that originate emission in hydrogen, helium, and/or metal lines.
These disks seem to be mainly generated by rapid rotation and/or binarity,
combined with non-radial pulsations (Huat et al., 2009; Neiner et al., 2012). 
These phenomena occur as an episode during the evolution of hot B-type stars.

One of the most intriguing properties of Be stars is their long-term variability, which 
seems to be related to disk growth or loss events (Hubert \& Floquet, 1998).
These events produce spectroscopic and photometric effects, i.e. changes from emission to 
absorption lines (and vice versa), and also flux and color variations.
Given the great variety of observed events, many open questions remain unanswered
(see the review by Porter \& Rivinius, 2003, and references therein), which raises the importance of studying these objects.
As the same authors state ``Be stars are in a unique position to make contributions to several 
important branches of stellar physics, e.g., asymmetric mass loss processes, stellar angular 
momentum distribution evolution, asteroseismology, and magnetic field evolution''.


The primary goal of this paper is to present the analysis carried out on a new possible transient Be star, 
labelled HD\,112999 ($\alpha_{J2000}=$13:01:35, $\delta_{J2000}= -$60:40:16). This star was observed 
by one of us (MAC) while trying to identify possible members of the Centaurus OB1 (CenOB1) stellar association (Corti \& Orellana, 2013). 
The spectral classification of this star varies depending on the bibliography available. 
It was first reported as a Be star by Bidelman \& MacConnell (1973). Other authors reported different spectral types, i.e. 
Cannon \& Pickering (B8; 1920), Houk \& Cowley (B6~III (N); 1975), and Garrison et al. (B6~V; 1977). Nowadays, HD\,112999 is listed in the BeSS 
catalogue\footnote{http://basebe.obspm.fr} as B6 III ne (Neiner et al., 2011).  
This star prompted further attention because our optical spectrum, taken on 2009, was very different from those classified before.
We consulted spectral and photometric databases and found that HD\,112999
is a variable Be star which seems to have experimented disk $-$ loss and growth $-$ events over the last decades. 
In the following sections, we describe these facts.



\section{Observational Data}
\subsection{Spectroscopic data}

The observational material belongs to different program runs obtained at the Complejo Astron\'omico El Leoncito (CASLEO), Argentina and La Silla Observatory,
Chile. Different instrumental configurations, detailed in Table~1, were used in these runs. 

For CASLEO observations, comparison arc images were observed
in the same sky position where the stellar images were located immediately after or before the stellar exposures,
being Th$-$Ar for the echelle mode of the REOSC spectrograph, Cu$-$Ar for the simple mode, and
He$-$Ne$-$Ar if the B\&C was used. Moreover, bias frames, standard stars of radial velocity, and spectral type 
were observed every night, the latter only during run B. 
We also took the spectrum of the standard of rotational velocity, $\tau$ Sco (Slettebak et al., 1975),
during run C. These spectra were processed and analysed with IRAF\footnote{
IRAF is distributed by the National Optical Astronomy Observatories, which are operated by
the Association of Universities for Research in Astronomy, Inc., under cooperative
agreement with the National Science Foundation.} routines.

The spectrum retrieved from the ESO database was obtained with the FEROS spectrograph and processed with the MIDAS pipeline. The radial velocities
were obtained by simple cross-correlation of the echelle orders of the HD\,112999 star and of the simultaneous calibration fiber with regard to the pertinent 
reference spectrum.

{
%\small
\begin{center}
\begin{table}
\caption{Instrumental configurations used}
\begin{tabular}{c@{\hskip3mm}l@{\hskip3mm}l@{\hskip3mm}c@{\hskip3mm}c@{\hskip3mm}c@{\hskip3mm}c@{\hskip3mm}c@{\hskip3mm}c@{\hskip3mm}c}
\hline
\hline
run &Observat. &Epoch(s)& HJD             &Telesc. & Spectrograph& Rec. & $\Delta\lambda$& exp.& S/N\\
  &   &    &    &     &    & disp. &  &time  &        \\
      &                     &                 & 2400000+ &         [m]     &                         & [\AA~px$^{-1}$] & [\AA]          &  [sec]      &        \\
\hline
\noalign{\hrule height 0.4pt}
A & La Silla/ESO & 2008 May  & 54603.68 & 2.2 & FEROS   &  0.03 & 3700-8600 &  600 &  70-120 \\
B & CASLEO & 2009 Apr. & 54941.70 & 2.1 & REOSC CD &  0.2 & 3700-6000 & 1200 & 20-50 \\
C & CASLEO & 2012 Jan. & 55930.86 & 2.1 & REOSC CD & 0.2 & 3700-6000 & 1200 & 20-50 \\
D & CASLEO & 2012 Apr. & 56047.66 & 2.1& REOSC SD& 1.6 & 5900-7400 & 700 & 150-200 	\\
E & CASLEO & 2012 June & 56086.00 & 2.1& Boller\&Chivens & 2.7 &   3500-5000 & 150 & 160-250  \\
\hline
\end{tabular}
\end{table}
\end{center}
%\normalsize
}

\subsection{Photometric data}

The photometric data were taken from two sources: the Epoch Photometry Annex of Hipparcos Astrometry 
Mission (Perryman \& ESA, 1997) and The All Sky Automated Survey (ASAS) (Pojmanski, 1997).

The Hipparcos data consist of 214 observations made between December 1989  and January 1993. 
The measurements are in the interval $7.31 < H_p < 7.48$; the errors of the individual 
measurements range from 0.007 to 0.020 mag. 
According to the criteria adopted when Hipparcos data were analysed, this star was classified as an 
``unsolved variable''\footnote{cf. The Hipparcos and Tycho Catalogues, Vol. 1, Introduction and 
Guide to the Data, Sec. 1.3 App. 2.}. 
Following the Hipparcos calibration for a star with colour index $V-I = 0.070$, as in this case, 
the relation $H_p - V_J = 0.025$ should hold, where $V_J$ is the magnitude in the $V$ filter of the 
Johnson photometric system.

The ASAS data include 1030 magnitude determinations obtained between November 2000 and December 2009.
ASAS provides aperture photometry with several apertures. For this study, the aperture labeled as MAG~1 in the 
dataset was selected because larger apertures could be contaminated by a neighbor star. The errors of individual measurements 
are up to 0.120 mag, with a typical value err$_{ASAS} = 0.040$ mag. 
Since err$_{ASAS} > (H_p - V_J)$, no zero-point correction was applied to compare the two datasets.

\section{Results}
\subsection{Spectral Analysis}

The FEROS spectrum (labelled A in Table~1) shows typical Be features such as the Balmer 
lines H$\gamma$, H$\beta$ and H$\alpha$ in emission (see Fig~2). There, at least one additional
emission line, Fe~{\sc i} $\lambda$4328 bluer than H$\gamma$, and two additional emission lines, 
Fe~{\sc i} $\lambda$4849 and Fe~{\sc i} $\lambda$4875 of H$\beta$, can be observed. The spectrum 
also presents other metallic lines, i.e. O~{\sc i\sc i}, Fe~{\sc i\sc i}, Cr~{\sc i\sc i}, Ti~{\sc i\sc i\sc i}, C~{\sc i\sc i\sc i},
etc, as weak emissions, some of them shown in Fig~1.
All of these emission lines could be originated in a disk.
A Be star with mid inclination angle might cause the double structure observed in H$\alpha$ emission lines. 
The rotation of the disk plus a possible absorption 
(``reversal" of the emission) against the edge of the star or disk cause such profiles of double structure. 
Other features as He~{\sc i}, $\lambda$4009, 4026, 4144, 4387, 4471, 4921, 5875, 6678 and 7065, 
Si~{\sc i\sc i} $\lambda\lambda$4128-30 and Mg~{\sc i\sc i} $\lambda$4481 can be observed in absorption. 
These lines are thought to be originated in the stellar photosphere. 
This composite spectrum indicates that the HD\,112999's disk was thick and extended during 2008 May. 

\IBVSfig{7cm}{6060-f1.eps}{Some metallic emission lines in the FEROS spectrum.}
\IBVSfigKey{6060-f1.eps}{HD 112999}{}

Our B spectrum, obtained about one year later than A, 
shows a very weak emission contribution in the H$\beta$ profile and an almost marginal one 
in the H$\gamma$ line. The metallic lines (seen as weak emissions in A) have not been detected in this spectrum.
We think that this is not due to the fact that the B spectrum has a poorer S/N ratio than A. The absorption lines, 
which would result from the stellar photosphere in the A spectrum, can also be observed here.
  
Three years later, the C spectrum presented the Balmer lines H$\gamma$ and H$\beta$ as pure absorption, 
i.e. there were no traces of emission contribution in these lines (see Fig.~2).

\begin{table}
\begin{center}
\caption{Radial velocities measured in the high resolution spectra}
\label{tab02}
\begin{tabular}{lccc}
\hline
Line & run A & run B & run C \\
 & [km s$^{-1}$] & [km s$^{-1}$] & [km s$^{-1}$] \\
\hline
He~I 4026 & $-$20 &   5 &     7  \\
He~I 4471 &  $-$35 & $-$15 & $-$31 \\
Mg~II  4481 & $-$92 & $-$5 & $-$2 \\
He~I 5876 &  $-$20 & 36 & $-$19 \\
Na~I 5890-96 & 4.5  & 5.5  & 2.5 \\
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSfig{12cm}{6060-f2.eps}{Variations of the H$\gamma$, H$\beta$ and H$\alpha$ lines from spectra obtained in 
different runs (see Table~1).
Other emission lines identified as 
Fe~{\sc i} $\lambda$ 4328 (in the H$\gamma$ region), 
Fe~{\sc i} $\lambda$ 4849 and $\lambda$ 4875 (H$\beta$ region), and
Fe~{\sc i} $\lambda$ 6574 (H$\alpha$ region) can also be observed.}
\IBVSfigKey{6060-f2.eps}{HD 112999}{}

The D spectrum was obtained by one of us (WAW) to see the profile of the H$\alpha$ line, as neither B nor C spectra
included it in their spectral ranges. 
Thus, we proved that H$\alpha$ is a conspicuous absorption line in the spectrum taken in
April 2012 (see Fig.~2). 

The E spectrum is the one we have been able to obtain more recently (Fig.~3).
 It shows the same absorption spectral lines than the other spectra, plus a very narrow absorption line 
 at 4233 \AA , which we have identified as Fe~{\sc ii}.
We argue that this line seems to have originated in a shell because its FWHM is $\sim2.5$ \AA\, compared to the 
FWHM $\sim8$ \AA\, of the photospheric He~{\sc i} absorption lines.    
This assumption is in good agreement with the fact that the forming region of 
Fe~{\sc ii} lines is located close to the central star  (Arias et al. 2006). 


We classified the Be-type spectra A, B, and E as B2$-$3~V, following the criteria of Walborn \& Fitzpatrick (1990),  
i.e. the ratio between Si~{\sc iii} $\lambda$4552 and Si~{\sc iv} $\lambda$4089, the
declining strengths of the C~{\sc iii}+O~{\sc ii} blends at $\lambda\lambda$4070 and 4650, and the weakness of all the Si~{\sc ii-iii} features.  
From the spectral type B2 to B3, Si~{\sc ii} $\lambda\lambda$4128-30, 
C~{\sc ii} $\lambda$4267 and Mg~{\sc ii} $\lambda$4481 increase in prominence. 
The very large He~{\sc i} $\lambda\lambda$4144/4121 ratio is a characteristic of the B2~V spectra and
the principal luminosity criterion is Si~{\sc iii} $\lambda$4552/ He~{\sc i} $\lambda$4387.


The projected rotational velocity ($v \sin i$) in this class of stars is an important parameter. To estimate it,
we used the spectrum of the star $\tau$ Sco, which was convolved with rotation line profiles calculated for different projected rotational velocities,
 and the \emph{FWHM} of the absorption line He~{\sc i} $\lambda$5015 was measured for each velocity.
Then, a linear relation between \emph{FWHM} and the $v \sin i$ was fitted. This empirical relation was used to translate the 
\emph{FWHM} of the line in the spectrum of HD~112999 into a $v \sin i$ estimation. 
In this way we obtained $v \sin i = 170 \pm 40$ km s$^{-1}$, the error being so large because of the low S/N ratio of the 
spectrum and the weakness of the line.

The B star becomes a Be star exhibiting rapid rotation probably as the result of disk instabilities caused by 
the spun up by binary mass transfer (McSwain et al., 2009). In order to know if this is the case for HD\,112999 star,
we measured the radial velocities in its three high-resolution spectra (A, B, and C). 
For this, we fitted Gaussian profiles to the selected spectral lines, 
i.e. He~{\sc i} $\lambda\lambda$4026, 4471 and 5876, and Mg~II $\lambda$4481, as well as the interstellar lines of Na {\sc i}. 
A comparison of the values of Na {\sc i} showed no systematic differences between the spectrographs 
used (within an error of 3 km s$^{-1}$), nevertheless, the He~{\sc i} and Mg~{\sc ii}  $\lambda$4481 
absorption lines present discrepancies within one spectrum which are much larger than for
any of these lines between different spectra. The observed differences between spectra cannot be exploited to
speculate a possible binarity, because the different values are expected from one
spectrum to another in the case of a binary star and all the lines should vary in the same way within one
spectrum. We provide the radial velocity measurements in Table 2 for future reference.

\subsubsection{BCD fundamental parameters}

\IBVSfig{9cm}{6060-f3.eps}{Balmer discontinuity: D is the first Balmer jump for normal B
star, d is the second discontinuity in absorption, indicating the
presence of the circumstellar envelope.}
\IBVSfigKey{6060-f3.eps}{HD 112999}{Be star}


Some physical properties from the E spectrum of HD\,112999 were derived by using the BCD 
(Barbier-Chalonge-Divan) spectrophotometric system (Chalonge \& Divan, 1973, 1977). 
A detailed description of this method is presented in Zorec et al. (2009, Appendix A) and further 
applications to Be stars were made by Zorec et al. (2005) and Aidelman et al. (2012). 
This method is ideal for studying peculiar stars, and in particular Be stars, due to the fact 
that the parameters defined by the method
are not affected by interstellar extinction and absorption/emission from the circumstellar 
envelope (Zorec \& Briot, 1991).
Then, we determined a B3 spectral type (with one subtype error) of
luminosity class III, an effective temperature $T_{\rm eff} = 17\,500 \pm 1\,000$~K, 
a surface gravity $log~g = 3.3 \pm$ 0.5, 
an absolute magnitude $M_V = -2.5 \pm$ 0.5 mag, 
and a color excess E$_{B-V} = 0.11 \pm$ 0.07 mag. 

The presence of the second Balmer discontinuity in the E spectrum indicates that
a circumstellar envelope can still be observed (Divan, 1979). Figure~3 
shows this spectrum in the Balmer discontinuity region, where the first jump, D, corresponds to a normal 
B star while the second one, d, is originated by the envelope.

Later on, we estimated the distance from HD~112999 to the Sun, using its extreme V magnitudes, i.e. 
7.3 $\leq$ V $\leq$ 7.5 (see Fig.~4), corrected by colour excess 
E$_{B-V} = 0.11 \pm$ 0.07 mag and considering the standard selective absorption coefficient, 
$R_{\mathrm v}$ = 3.1 (Schultz \& Wiemer, 1975). 
We obtained a distance modulus of 9.5 $\pm$ 0.5 mag (790 $\pm$ 180 pc) and 9.7 $\pm$ 0.5 mag (870 $\pm$ 200 pc), respectively. 
These estimated distance values with their respective errors are slightly larger than the Hipparcos distance (654 pc). 
Then, HD\,112999 is closer than the Cen\,OB1 association, $V_0 - M_v$ = 12 mag (2500 pc) (Corti et al., 2012).

\subsection{Light curve analysis}

\IBVSfig{9cm}{6060-f4.eps}{Light curve of HD\,112999. Boxes and asterisks correspond to Hipparcos and ASAS data, respectively. 
Filled circles depict the average magnitude in about 114 days. 
The capital letters (see Table~1) show the almost temporal coincidence between the photometric and spectroscopic data explained in section 3.2.}
\IBVSfigKey{6060-f4.eps}{HD 112999}{light curve}


The collected photometric data were analysed together and the resulting light curve is shown in 
Fig.~4. HD\,112999 presents two kinds of variabilities:  
short-term one (1.302 days; Hubert \& Floquet, 1998) and long-term one ($\sim$ years). 
The formerone with an amplitude smaller than 0.1 mag, is included in the Hipparcos data (see Fig.~5), and
it is the reason why this star has been included in the General Catalogue of Variable Stars  
(Samus et al., 2009) and classified as BE\footnote{Due to the type of variability, BE is used when a Be variable cannot be readily described 
as a Gamma Cassiopeiae variable (GCAS) star, (Samus et al. 2009)}.

\IBVSfig{9cm}{6060-f5.eps}{Hipparcos data showing variability smaller than 0.1 mag with a period $\sim$ 1 day.}
\IBVSfigKey{6060-f5.eps}{HD 112999}{light curve}

The long-term variation can be better observed in the ASAS data.  
To enhance and show it more clearly, we represent unweighted averages  
(calculated within intervals of $\sim$114 days) with filled circles. 
In Fig.~4 we identified the light maximum reached around HJD 2\,454\,200 (ASAS data). 

\section {Discussion}

The collected spectra show important variations, especially noticeable in the Balmer lines, i.e.  
their emission profiles decrease in intensity from May 2008 to June 2012 (A to E). 
Similar variability was already detected in other Be stars like MG\,31 and MG\,119 
in NGC\,3766 (McSwain et al., 2008); Pleione and $\kappa$~Dra (Hubert \& Floquet, 1998) and 66~Ophiuchi (Floquet et al., 2002). 

The relation between the photometric and spectroscopic data is shown in Fig.~4.
The capital letters are the same defined in Table~1. 
The light curve and the spectra obtained in A and B runs, are well correlated in the sense that as the 
star fades, 
the Balmer emissions decrease their intensities (Fig.~2). This behavior is
related to disk dissipation. The lack of photometric data after 2009 August prevents us to determine 
if the star reached the minimum between B and C runs or it will be reached later.

The behavior observed in HD\,112999 led us to search in the existing literature for more information about this star. Thus, we learned that the
only Be spectrum of HD\,112999 was obtained in the period 1967$-$1969 by Bidelman \& MacConnell (1973)\footnote{
This observation was the reason to be included in the Catalogue of Be Stars (Jaschek \& Egret, 1982)}.
Unfortunately, they did not provide a precise date of observation.
As already mentioned in Section~1, other authors have reported different spectral classifications for HD\,112999.
We adopted the B2$-$3~V spectral type for HD\,112999, which was determined following the criteria of Walborn \& Fitzpatrick (1990).

\section{Summary}

The analysis of the spectroscopic and photometric data of HD\,112999 allowed us to identify 
a long-term variability in its $V$ light curve and the change of the Balmer
line profiles from emission to absorption. The decline in $V$ magnitudes between 2007 and 2009 
is related to the disappearance of emission lines, very noticeable in some Balmer lines.
We propose that the reported changes are induced by the loss of the disk.
Photometric data were not sufficient to search for long-term periodicities; therefore, we encourage other
researchers to monitor this star in the future. 
We classified our spectra as B2$-$3, the luminosity class should be clarified with further 
observations. 

We used the observations obtained in different observing programs to measure some
important parameters such as the projected rotational velocity and the distance modulus.  
Also, our last spectrum E, obtained in June 2012, was analysed with the BCD method, from which we noted 
that a circumstellar envelope is still present. Hence, further spectra should be obtained to 
determine if HD\,112999 will reach a normal B-type. \\

\noindent ACKNOWLEDGMENTS:
This research used of the SIMBAD database, operated at CDS, Strasbourg, France, and also
the WEBDA database, operated at the Institute of Astronomy of the University of Vienna.
This paper was partially supported  by Consejo Nacional de Investigaciones 
Cient\'{\i}ficas y T\'ecnicas {\rm CONICET} under projects {\rm PIP} 
01299 and 0523 and by Universidad Nacional de La Plata ({\rm UNLP})
under project G091. We are very grateful to Dra. Granada Anah\'{\i} and
Dra. Cidale Lydia for their interesting and valuable comments. We thank Mrs Roxana Kotton 
and the English Department of FCAyG (UNLP) for a careful reading of the manuscript. 

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\end{document}
