92 research outputs found
Trumpler 16-26: A New Centrifugal Magnetosphere Discovered via SDSS/APOGEE H-band Spectroscopy
We report the discovery of a new example of the rare class of highly
magnetized, rapidly rotating, helium enhanced, early B stars that produce
anomalously wide hydrogen emission due to a centrifugal magnetosphere (CM). The
star is Trumpler 16-26, a B1.5 V member of the Trumpler 16 open cluster. A CM
was initially suspected based on hydrogen Brackett series emission observed in
SDSS/APOGEE -band spectra. Similar to the other stars of this type, the
emission was highly variable and at all times remarkable due to the extreme
velocity separations of the double peaks (up to 1300 km s.) Another clue
lay in the TESS lightcurve, which shows two irregular eclipses per cycle when
phased with the likely 0.9718115 day rotation period, similar to the behavior
of the well known CM host star Ori E. To confirm a strong magnetic
field and rotation-phase-locked variability, we initiated a follow-up campaign
consisting of optical spectropolarimetry and spectroscopy. The associated data
revealed a longitudinal magnetic field varying between and kG
with the period found from photometry. The optical spectra confirmed rapid
rotation ( km s), surface helium enhancement, and wide,
variable hydrogen emission. Tr16-26 is thus confirmed as the 20
known, the fourth most rapidly rotating, and the faintest CM host star yet
discovered. With a projected dipole magnetic field strength of
kG, Tr16-26 is also among the most magnetic CM stars
High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles
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. 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%. We focus 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 ~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. 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
IN-SYNC. V. Stellar kinematics and dynamics in the Orion A Molecular Cloud
The kinematics and dynamics of young stellar populations enable us to test
theories of star formation. With this aim, we continue our analysis of the
SDSS-III/APOGEE IN-SYNC survey, a high resolution near infrared spectroscopic
survey of young clusters. We focus on the Orion A star-forming region, for
which IN-SYNC obtained spectra of stars. In Paper IV we used these
data to study the young stellar population. Here we study the kinematic
properties through radial velocities (). The young stellar population
remains kinematically associated with the molecular gas, following a
gradient along filament. However, near the center
of the region, the distribution is slightly blueshifted and asymmetric;
we suggest that this population, which is older, is slightly in foreground. We
find evidence for kinematic subclustering, detecting statistically significant
groupings of co-located stars with coherent motions. These are mostly in the
lower-density regions of the cloud, while the ONC radial velocities are
smoothly distributed, consistent with it being an older, more dynamically
evolved cluster. The velocity dispersion varies along the filament.
The ONC appears virialized, or just slightly supervirial, consistent with an
old dynamical age. Here there is also some evidence for on-going expansion,
from a --extinction correlation. In the southern filament, is
-- times larger than virial in the L1641N region, where we infer a
superposition along the line of sight of stellar sub-populations, detached from
the gas. On the contrary, decreases towards L1641S, where the
population is again in agreement with a virial state.Comment: 14 pages, 13 figures, ApJ accepte
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