K- and L-band spectroscopy of Be stars (original) (raw)
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The Astronomical Journal, 2014
The Apache Point Galactic Evolution Experiment (APOGEE) has amassed the largest ever collection of multi-epoch, high-resolution (R ∼ 22, 500), H-band spectra for B-type emission line (Be) stars. These stars were targeted by APOGEE as telluric standard stars and subsequently identified via visual inspection as Be stars based on H i Brackett series emission or shell absorption in addition to otherwise smooth continua and occasionally non-hydrogen emission features. The 128/238 APOGEE Be stars for which emission had never previously been reported serve to increase the total number of known Be stars by ∼ 6%. Because the H-band is relatively unexplored compared to other wavelength regimes, we focus here on identification of the H-band lines and analysis of the emission peak velocity separations (∆v p) and emission peak intensity ratios (V/R) of the usually double-peaked H i and non-hydrogen emission lines. H i Br11 emission is found to preferentially form in the circumstellar disks at an average distance of ∼2.2 stellar radii. Increasing ∆v p toward the weaker Br12-Br20 lines suggests these lines are formed interior to Br11. By contrast, the observed IR Fe ii emission lines present evidence of having significantly larger formation radii; distinctive phase lags between IR Fe ii and H i Brackett emission lines further supports that these species arise from different radii in Be disks. Several emission lines have been identified for the first time including C i 16895, a prominent feature in the spectra for almost a fifth of the sample and, as inferred from relatively large ∆v p compared to the Br11-Br20, a tracer of the inner regions of Be disks. Emission lines at 15760Å and 16781Å remain unidentified, but usually appear along with and always have similar line profile morphology to Fe ii 16878. Unlike the typical metallic lines observed for Be stars in the optical, the H-band metallic lines, such as Fe ii 16878, never exhibit any evidence of shell absorption, even when the H i lines are clearly shell-dominated. The first known example of a quasi-triple-peaked Br11 line profile is reported for HD 253659, one of several stars exhibiting intra-and/or extra-species V/R and radial velocity variation within individual spectra. Br11 profiles are presented for all discussed stars, as are full APOGEE spectra for a portion of the sample.
Properties of the Hα‐emitting Circumstellar Regions of Be Stars
The Astrophysical Journal, 2005
Long-baseline interferometric observations obtained with the Navy Prototype Optical Interferometer of the Hα-emitting envelopes of the Be stars η Tauri and β Canis Minoris are presented. For compatibility with the previously published interferometric results in the literature of other Be stars, circularly symmetric and elliptical Gaussian models were fitted to the calibrated Hα observations. The models are sufficient in characterizing the angular distribution of the Hα-emitting circumstellar material associated with these Be stars. To study the correlations between the various model parameters and the stellar properties, the model parameters for η Tau and β CMi were combined with data for other Be stars from the literature. After accounting for the different distances to the sources and stellar continuum flux levels, it was possible to study the relationship between the net Hα emission and the physical extent of the Hα-emitting circumstellar region. A clear dependence of the net Hα emission on the linear size of the emitting region is demonstrated -2and these results are consistent with an optically thick line emission that is directly proportional to the effective area of the emitting disk. Within the small sample of stars considered in this analysis, no clear dependence on the spectral type or stellar rotation is found, although the results do suggest that hotter stars might have more extended Hα-emitting regions.
Line Variations of Hα Emissions and Absorptions of Be Stars
Journal of Physics: Conference Series
We present the spectroscopic variations of 14 program Be stars observed within 2008-2009 at the Bosscha Observatory, Lembang, Indonesia. The Be stars show spectroscopic profiles as Be and Be-shell, and sometimes as B-normal. These profiles come from the disk-like envelope or rings surrounded the star's equatorial plane. Our program stars are: 5 as Be singlepeaked, 2 as Be double-peak, and 7 as B-normal stars. We also measure the Ip/Ic ratio from the line profiles.
Astronomy and Astrophysics Supplement Series, 2000
We present here the Hα spectra of 44 Be stars taken at a resolution of 0.5Å. From the spectra, different emission line parameters have been deduced. A study of the correlations between different pairs of these parameters has been made with a view to understanding the mechanisms of line formation and shaping in Be stars.
Comparison of the Hαcircumstellar disks in Be/X-ray binaries and Be stars
Astronomy & Astrophysics, 2001
We present a comparative study of the circumstellar disks in Be/X-ray binaries and isolated Be stars based upon the Hα emission line. From this comparison it follows that the overall structure of the disks in the Be/X-ray binaries is similar to the disks of other Be stars, i.e. they are axisymmetric and rotationally supported. The factors for the line broadening (rotation and temperature) in the disks of the Be stars and the Be/X-ray binaries seem to be identical. However, we do detect some intriguing differences between the envelopes. On average, the circumstellar disks of the Be/X-ray binaries are twice as dense as the disks of the isolated Be stars. The different distribution of the Be/X-ray binaries and the Be stars seen in the full width half maximum versus peak separation diagram indicates that the disks in Be/X-ray binaries have on average a smaller size, probably truncated by the compact object.
First spectro-interferometric survey of Be stars
Astronomy & Astrophysics, 2012
Context. Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed infrared-excess and emission lines. The phenomena involved in the disk formation still remain highly debated. Aims. To progress in the understanding of the physical process or processes responsible for the mass ejections and test the hypothesis that they depend on the stellar parameters, we initiated a survey on the circumstellar environment of the brightest Be stars. Methods. To achieve this goal, we used spectro-interferometry, the only technique that combines high spectral (R=12000) and high spatial (θ min =4 mas) resolutions. Observations were carried out at the Paranal observatory with the VLTI/AMBER instrument. We concentrated our observations on the Brγ emission line to be able to study the kinematics within the circumstellar disk. Our sample is composed of eight bright classical Be stars : α Col, κ CMa, ω Car, p Car, δ Cen, µ Cen, α Ara, and o Aqr. Results. We managed to determine the disk extension in the line and the nearby continuum for most targets. We also constrained the disk kinematics, showing that it is dominated by rotation with a rotation law close to the Keplerian one. Our survey also suggests that these stars are rotating at a mean velocity of V/V c = 0.82 ± 0.08. This corresponds to a rotational rate of Ω/Ω c = 0.95 ± 0.02 Conclusions. We did not detect any correlation between the stellar parameters and the structure of the circumstellar environment. Moreover, it seems that a simple model of a geometrically thin Keplerian disk can explain most of our spectrally resolved K-band data. Nevertheless, some small departures from this model have been detected for at least two objects (i.e, κ CMa and α Col). Finally, our Be stars sample suggests that rotation is the main physical process driving the mass-ejection. Nevertheless, smaller effects from other mechanisms have to be taken into account to fully explain how the residual gravity is compensated.
Be stars are hot stars exhibiting the so-called Be p
2005
Received; accepted Abstract. We present the first VLTI/MIDI observations of the Be star α Ara, showing a nearly unresolved circumstellar disk in the N band. The interferometric measurements made use of the UT1 and UT3 telescopes. The projected baselines were 102 and 74 meters with position angles of 7 ◦ and 55 ◦ , respectively. These measurements put an upper limit to the envelope size in the N band under the Uniform disk approximation of φmax = 4±1.5 mas, corresponding to 14 R⋆, assuming R⋆=4.8R ⊙ and the Hipparcos distance of 74 pc. On the other hand the disk density must be large enough to produce the observed strong Balmer line emission. In order to estimate the possible circumstellar and stellar parameters we have used the SIMECA code developed by Stee (1995) and Stee & Bittar (2001). Optical spectra taken with the échelle instrument Heros and the ESO-50cm telescope, as well as infrared ones from the 1.6m Brazilian telescope have been used together with the MIDI spectra and vis...
Photometric and spectroscopic variations of the Be star HD 112999
Be objects are stars of B spectral type showing lines of the Balmer series in emission. The presence of these lines is attributed to the existence of an extended envelope, disk type, around them. Some stars are observed in both the Be and normal B-type spectroscopic states and they are known as transient Be stars. In this paper we show the analysis carried out on a new possible transient Be star, labelled HD 112999, using spectroscopic optical observations and photometric data.
Far-infrared Excesses in Classical Be Stars
International Astronomical Union Colloquium
A sample of Be stars with large far-infrared excesses detected by IRAS is selected and their high-resolution IRAS images are examined. The far-infrared emission from most of them is marginally extended and is associated with the optical sources. Modeling of the stars’ spectral energy distributions allows us to rule out the infrared cirrus nature of the excesses. We suggest that the excesses are more likely due to circumstellar dust, possibly formed early in the evolution of the star.