HIGH-RESOLUTION H-BAND SPECTROSCOPY OF Be STARS WITH SDSS-III/APOGEE. I. NEW Be STARS, LINE IDENTIFICATIONS, AND LINE PROFILES

Abstract

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.

Stellar parameters of Be stars observed with X-shooter

“…-HIP 28561 (HD 40724, HR 2116) is the brightest newly identified Be star among the ABE sample of Chojnowski et al (2015). This object shows a double BD in emission and Mennickent & Vogt (1988) with v sin i = 300 km s −1 .…”

“…Photometric studies show that earlier type Be stars are more likely to be variable (e.g., Hubert & Floquet 1998). Chojnowski et al (2015) have demonstrated that Be stars can often be found among stars observed for the purpose of removing telluric absorption in the near-infrared domain because main sequence B stars are among the preferred objects for this task. Inspired by this example, we decided to search for Be stars in a similarly extensive database of telluric standard star observations, namely that taken at the Very Large Telescope (VLT) with the X-shooter instrument.…”

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

“…Thirty-five of the bluest and brightest stars evenly distributed across the field are chosen for telluric absorption calibration (see Section 5 and Figure 8 of Zasowski et al 2013). Although not originally envisioned as part of the primary science focus of APOGEE, the number of hot stars targeted and the ample spectral time series collected for many has turned out to yield a number of interesting science results, particularly in the study of emission line (B[e]) stars and other, non-emission stars with circumstellar disks (Chojnowski et al 2015, see Section 7.4.1 and Figure 22) and including the discovery of rare stellar types (Eikenberry et al 2014). …”

“…For instance, Figure 21 shows an example of a double-lined spectroscopic binary made evident through the multi-epoch spectroscopy). As another example of the interesting phenomena that a detailed exploration of APOGEE's time series spectral data might uncover, Figure 22 shows the strong variation in a Brackett series line for one of the numerous Be stars discovered by APOGEE (Chojnowski et al 2015) within the sample of hot stars observed for telluric absorption correction.…”

A CATALOG OF 1.5273 μm DIFFUSE INTERSTELLAR BANDS BASED ON APOGEE HOT TELLURIC CALIBRATORS

“…To do so we used the Chojnowski et al (2015) catalog of Be stars and the information contained in the APOGEE tables. All these spectra have been the subject of one by one visual inspection and only those where the DIB was clearly unambiguously and accurately detected were kept.…”