97 research outputs found
High resolution spectroscopy of the BCD galaxy Haro 15:I. Internal kinematics
Using echelle spectroscopy, obtained at Las Campanas Observatory, we present
a detailed study of the internal kinematics of the nebular material in multiple
knots of the blue compact dwarf galaxy Haro 15. A detailed analysis of the
complex emission line profiles show the presence of an underlying broad
component in almost all knots, and the brightest star-forming region shows
unmistakable signs for the presence of two distinct narrow kinematical
components. We also study the information that our analysis provides regarding
the motion of the individual knots in the Haro 15 galaxy potential, confirming
that they follow galactic rotation. Finally, we examine the relation between
their velocity dispersion and luminosity, finding that almost all knots follow
the relation for virialised systems. This holds for the strong narrow
components identified in complex fits and for single profile fits, although the
latter show a flatter slope. In agreement with previous findings, in this paper
we show that the existence of multiple kinematical components among massive
starbursts cannot be overlooked, as it has a noticeable effect on any
subsequent analysis that relies on basic parameters.Comment: 12 pages, 21 figure
Limits to Transits of the Neptune-mass planet orbiting Gl 581
We have monitored the Neptune-mass exoplanet-hosting M-dwarf Gl 581 with the
1m Swope Telescope at Las Campanas Observatory over two predicted transit
epochs. A neutral density filter centered at 550nm was used during the first
epoch, yielding 6.33 hours of continuous light curve coverage with an average
photometric precision of 1.6 mmags and a cadence of 2.85 min. The second epoch
was monitored in B-band over 5.85 hours, with an average photometric precision
of 1.2 mmags and 4.28 min cadence. No transits are apparent on either night,
indicating that the orbital inclination is less than 88.1 deg for all planets
with radius larger than 0.38 R_Nep = 1.48 R_Earth. Because planets of most
reasonable interior composition have radii larger than 1.55 R_Earth we place an
inclination limit for the system of 88.1 deg. The corresponding minimum mass of
Gl 581b remains 0.97 M_Nep = 16.6 M_Earth.Comment: 7 pages, 2 figures, 1 table, to appear in PAS
Constraints on the Binarity of the WN3/O3 Class of Wolf-Rayet Stars
The WN3/O3 Wolf-Rayet (WR) stars were discovered as part of our survey for
WRs in the Magellanic Clouds. The WN3/O3s show the emission lines of a
high-excitation WN star and the absorption lines of a hot O-type star, but our
prior work has shown that the absorption spectrum is intrinsic to the WR star.
Their place in the evolution of massive stars remains unclear. Here we
investigate the possibility that they are the products of binary evolution.
Although these are not WN3+O3~V binaries, they could still harbor unseen
companions. To address this possibility, we have conducted a multi-year radial
velocity study of six of the nine known WN3/O3s. Our study finds no evidence of
statistically significant radial velocity variations, and allows us to set
stringent upper limits on the mass of any hypothetical companion star: for
probable orbital inclinations, any companion with a period less than 100 days
must have a mass less than 2Mo. For periods less than 10 days, any companion
would have to have a mass less than 1Mo. We argue that scenarios where any such
companion is a compact object are unlikely. The absorption lines indicate a
normal projected rotational velocity, making it unlikely that these stars
evolved with the aid of a companion star that has since merged. The modest
rotation also suggests that these stars are not the result of homogenous
evolution. Thus it is likely that these stars are a normal but short-lived
stage in the evolution of massive stars.Comment: Astrophysical Journal in pres
The Physical Properties and Effective Temperature Scale of O-type Stars as a Function of Metallicity. III. More Results from the Magellanic Clouds
In order to better determine the physical properties of hot, massive stars as
a function of metallicity, we obtained very high SNR optical spectra of 26 O
and early B stars in the Magellanic Clouds. These allow accurate modeling even
in cases where the He I 4471 line has an equivalent width of only a few tens of
mA. The spectra were modeled with FASTWIND, with good fits obtained for 18
stars; the remainder show signatures of being binaries. We include stars in
common to recent studies to investigate possible systematic differences. The
"automatic" FASTWIND modeling method of Mokiem and collaborators produced
temperatures 1100 K hotter on the average, presumably due to the different
emphasis given to various temperature-sensitive lines. More significant,
however, is that the automatic method always produced some "best" answer, even
for stars we identify as composite (binaries). The temperatures found by the
TLUSTY/CMFGEN modeling of Bouret, Heap, and collaborators yielded temperatures
1000 K cooler than ours, on average. Significant outliers were due either to
real differences in the data (some of the Bouret/Heap data were contaminated by
moonlight continua) or the fact we could detect the HeI line needed to better
constrain the temperature. Our new data agrees well with the effective
temperature scale we presented previously. We confirm that the "Of"
emission-lines do not track luminosity classes in the exact same manner as in
Milky Way stars. We revisit the the issue of the "mass discrepancy", finding
that some of the stars in our sample do have spectroscopic masses that are
significantly smaller than those derived from stellar evolutionary models. We
do not find that the size of the mass discrepancy is simply related to either
effective temperature or surface gravity.Comment: ApJ, in pres
High-resolution spectroscopy of the blue compact dwarf galaxy Haro 15 – I. Internal kinematics
This is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Firpo, V., Bosch, G., Hägele, G.F., Díaz, A.I. and N. Morrell. High-resolution spectroscopy of the blue compact dwarf galaxy Haro 15 –I. Internal kinematics. Monthly Notices of the Royal Astronomical Society 414 (2011): 3288-329
On the multiplicity of the zero-age main-sequence O star Herschel 36
We present the analysis of high-resolution optical spectroscopic observations
of the zero-age main-sequence O star Herschel 36 spanning six years. This star
is definitely a multiple system, with at least three components detected in its
spectrum. Based on our radial-velocity (RV) study, we propose a picture of a
close massive binary and a more distant companion, most probably in wide orbit
about each other. The orbital solution for the binary, whose components we
identify as O9 V and B0.5 V, is characterized by a period of 1.5415 +/- 0.0006
days. With a spectral type O7.5 V, the third body is the most luminous
component of the system and also presents RV variations with a period close to
498 days. Some possible hypotheses to explain the variability are briefly
addressed and further observations are suggested.Comment: 6 pages, 2 figure
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