22 research outputs found
The B[e] phenomenon in the Milky Way and Magellanic Clouds
Discovered over 30 years ago, the B[e] phenomenon has not yet revealed all
its puzzles. New objects that exhibit it are being discovered in the Milky Way,
and properties of known objects are being constrained. We review recent
findings about objects of this class and their subgroups as well as discuss new
results from studies of the objects with yet unknown nature. In the Magellanic
Clouds, the population of such objects has been restricted to supergiants. We
present new candidates with apparently lower luminosities found in the LMC.Comment: 5 pages, 2 figures, IAU Symposium 272, Active OB stars: structure,
evolution, mass loss and critical limit
Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars
We report the results for rotational velocities, Vrot sin i, and macroturbulence dispersions, ζRT, for 12 metal-poor field red giant branch (RGB) stars and 7 metal-poor field red horizontal branch (RHB) stars. The results are based on Fourier transform
Rotation and Macroturbulence in Metal-poor Field Red Giant and Red Horizontal Branch Stars
We report the results for rotational velocities, Vrot sin i, and
macroturbulence dispersion, zeta(RT), for 12 metal-poor field red giant branch
stars and 7 metal-poor field red horizontal branch stars. The results are based
on Fourier transform analyses of absorption line profiles from high-resolution
(R ~ 120,000), high-S/N (~ 215 per pixel) spectra obtained with the Gecko
spectrograph at CFHT. We find that the zeta(RT) values for the metal-poor RGB
stars are very similar to those for metal-rich disk giants studied earlier by
Gray and his collaborators. Six of the RGB stars have small rotational values,
less than 2.0 km/sec, while five show significant rotation, over 3 km/sec. The
fraction of rapidly rotating RHB stars is somewhat lower than found among BHB
stars. We devise two empirical methods to translate the line-broadening results
obtained by Carney et al. (2003, 2008) into Vrot sin i for all the RGB and RHB
stars they studied. Binning the RGB stars by luminosity, we find that most
metal-poor field RGB stars show no detectable sign, on average, of rotation.
However, the most luminous stars, with M(V) <= -1.5, do show net rotation, with
mean values of 2 to 4 km/sec, depending on the algorithm employed, and these
stars also show signs of radial velocity jitter and mass loss.Comment: accepted for publication in the Astronomical Journa
Stable and Unstable Regimes of Mass Accretion onto RW Aur A
We present monitoring observations of the active T Tauri star RW Aur, from
2010 October to 2015 January, using optical high-resolution (R>10000)
spectroscopy with CFHT-ESPaDOnS. Optical photometry in the literature shows
bright, stable fluxes over most of this period, with lower fluxes (by 2-3 mag.)
in 2010 and 2014. In the bright period our spectra show clear photospheric
absorption, complicated variation in the Ca II 8542 A emission}profile shapes,
and a large variation in redshifted absorption in the O I 7772 and 8446 A and
He I 5876 A lines, suggesting unstable mass accretion during this period. In
contrast, these line profiles are relatively uniform during the faint periods,
suggesting stable mass accretion. During the faint periods the photospheric
absorption lines are absent or marginal, and the averaged Li I profile shows
redshifted absorption due to an inflow. We discuss (1) occultation by
circumstellar material or a companion and (2) changes in the activity of mass
accretion to explain the above results, together with near-infrared and X-ray
observations from 2011-2015. Neither scenario can simply explain all the
observed trends, and more theoretical work is needed to further investigate
their feasibilities.Comment: 23 pages, 11 figures, 4 tables, accepted by Astrophysical Journal;
some typos corrected on 4/18/201
The Polarizing Power of the Interstellar Medium in Taurus
We present a study of the polarizing power of the dust in cold dense regions
(dark clouds) compared to that of dust in the general interstellar medium
(ISM). Our study uses new polarimetric, optical, and spectral classification
data for 36 stars to carefully study the relation between polarization
percentage (p) and extinction (A_V) in the Taurus dark cloud complex. We find
two trends in our p-A_V study: (1) stars background to the warm ISM show an
increase in p with A_V; and (2) the percentage of polarization of stars
background to cold dark clouds does not increase with extinction. We detect a
break in the p-A_V relation at an extinction 1.3 +/- 0.2 mag, which we expect
corresponds to a set of conditions where the polarizing power of the dust
associated with the Taurus dark clouds drops precipitously. This breakpoint
places important restrictions on the use of polarimetry in studying
interstellar magnetic fields.Comment: 17 pages, 2 figures, to appear in ApJLett, AASTeX was use
Stable and Unstable Regimes of Mass Accretion onto RW Aur A
We present monitoring observations of the active T Tauri star RW Aur, from 2010 October to 2015 January, using
optical high-resolution (R 10,000) spectroscopy with Canada–France–Hawaii Telescope/ESPaDOnS. Optical
photometry in the literature shows bright, stable fluxes over most of this period, with lower fluxes (by 2–3 mag) in
2010 and 2014. In the bright period our spectra show clear photospheric absorption, complicated variation in the
Ca II λ8542 emission profile shapes, and a large variation in redshifted absorption in the O I λλ7772 and 8446 and
He I λ5876 lines, suggesting unstable mass accretion during this period. In contrast, these line profiles are
relatively uniform during the faint periods, suggesting stable mass accretion. During the faint periods, the
photospheric absorption lines are absent or marginal, and the averaged Li I profile shows redshifted absorption due
to an inflow. We discuss (1) occultation by circumstellar material or a companion and (2) changes in the activity of
mass accretion to explain the above results, together with near-infrared and X-ray observations from 2011 to 2015.
Neither scenario can simply explain all the observed trends, and more theoretical work is needed to further
investigate their feasibilities