In:
The Astronomical Journal, American Astronomical Society, Vol. 149, No. 1 ( 2015-01-01), p. 7-
Abstract:
The Apache Point Observatory 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 ( ) 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 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 compared to the Br11–Br20, a tracer of the inner regions
of Be disks. Emission lines at 15760 Å and 16781 Å 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.
Type of Medium:
Online Resource
ISSN:
0004-6256
,
1538-3881
DOI:
10.1088/0004-6256/149/1/7
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2015
detail.hit.zdb_id:
2207625-6
detail.hit.zdb_id:
2003104-X
SSG:
16,12
