225 research outputs found
Improved distances to several Galactic OB associations
Based on uvbybeta photometry we study the structure of several Galactic
star-forming fields. Lac OB1 is a compact association at 520+/-20 pc spatially
correlated with a region of intense HII emission in Sh2-126. Loden 112 is a
compact OB group at 1630+/-82 pc, probably connected to an extended feature of
OB stars located toward the Carina tangent. The field toward Car OB1 is complex
and likely contains apparent concentrations representing parts of long segments
of the Carina arm projected along the line of sight. Within the classical Mon
OB2 association we separate a relatively compact group at 1.26 kpc, that is
spatially correlated to the Monoceros Loop SN remnant.Comment: 6 pages, 4 figures, proceedings of "Stellar Clusters and Associations
- A RIA workshop on GAIA", 23-27 May 2011, Granada, Spai
Revised distances to several Bok globules
Distances to Bok globules and small dark nebulae are important for a variety
of reasons. We provide new distance estimates to several small clouds, some of
them known to harbor YSO and molecular outflows, and thus being of particular
interest. We use a procedure based on extinctions determined from the (H-K) vs.
(J-H) diagram, and stellar distances based on a Hipparcos calibration of the
main sequence locus: . The cloud confinement on the sky is
determined from contours of the average (H-K) color formed in reseaus. Along
the sight line stars affected by the clouds extinction may be extracted from
the variation of the number density of atomic hydrogen to provide the cloud distance and its uncertainty.
According to our estimates, the group of three globules CB24, CB25 and CB26 is
located at 407+/-27 pc, farther than the previous estimates. CB245 and CB246
are found at 272+/-20 pc, suggesting that the current distance to these clouds
is underestimated. Toward CB244 we detect a layer at 149+/-16 pc and the cloud
at 352+/-18, in good agreement with previous studies. CB52 and CB54, though to
be at 1500 pc, are found at 421+/-28 pc and slightly beyond 1000 pc,
respectively. It seems that the most distant Bok globule known, CB3, is located
at about 1400 pc, also significantly closer than currently accepted.Comment: 9 pages, 12 figures, submitted to A&
The field of Loden 112
Based on the available uvbybeta photometry of OB stars in the longitude range
281 - 285 deg in the Galactic disk, we identify a feature of young stars at
1630+/-82 pc, that is probably connected to the compact cluster candidate Loden
112 and the open cluster IC 2581. This feature seems to be spatially correlated
to RCW 48 and RCW 49 and several other smaller HII regions.Comment: 2 pages, 1 figure, proceedings of "Stellar Clusters and Associations
- A RIA workshop on GAIA", 23-27 May 2011, Granada, Spai
Massive Stellar Content of the Galactic Supershell GSH 305+01-24
The distribution of OB stars along with that of H, CO, dust
infrared emission, and neutral hydrogen is carried out in order to provide a
more complete picture of interactions of the young massive stars and the
observed supershell GSH 305+01-24. The studied field is located between
and . The
investigation is based on nearly 700 O-B9 stars with photometry
currently available. The derived stellar physical parameters were used to
establish a homogeneous scale for the distances and extinction of light for
major apparent groups and layers of foreground and background stars in
Centaurus and study the interaction with the surrounding interstellar medium.
The distance to the entire Centaurus star-forming complex is revised and a
maximum of the OB-star distance distribution is found at 1.80.4 (r.m.s)
kpc. The massive star component of GSH 305+01-24 is identified at about 85-90 %
completeness up to 11.5-12 mag. The projected coincidence of the OB stars with
the shell and the similarities between the shell's morphology and the OB-star
distribution indicate a strong interaction of the stellar winds with the
superbubble material. We demonstrate that these stars contribute a sufficient
wind injection energy in order to explain the observed size and expansion
velocity of the supershell. The derived stellar ages suggest an age gradient
over the Coalsack Loop. A continuous star-formation might be taking place
within the shell with the youngest stars located at its periphery and the open
cluster NGC 4755 being the oldest. A layer of very young stars at 1 kpc is
detected and its connection to both GSH 305+01-24 and the foreground GSH
304-00-12 H I shells is investigated.Comment: Accepted for publication in A&A. Paper consists of 11 pages, 3 tables
and 9 figures. Table 1 and Table 3 will only be available from CD
The Structure and the Distance of Collinder 121 from Hipparcos and Photometry: Resolving the Discrepancy
We present further arguments that the Hipparcos parallaxes for some of the
clusters and associations represented in the Hipparcos catalog should be used
with caution in the study of the Galactic structure. It has been already shown
that the discrepancy between the Hipparcos and ground based parallaxes for
several clusters including the Pleiades, Coma Ber and NGC 6231 can be resolved
by recomputing the Hipparcos astrometric solutions with an improved algorithm
diminishing correlated errors in the attitude parameters. Here we present new
parallaxes obtained with this algorithm for another group of stars with
discrepant data - the galactic cluster Cr 121. The original Hipparcos
parallaxes led de Zeeuw et al. to conclude that Cr 121 and the surrounding
association of OB stars form a relatively compact and coherent moving group at
a distance of 550 -- 600 pc. Our corrected parallaxes reveal a different
spatial distribution of young stellar populace in this area. Both the cluster
Cr 121 and the extended OB association are considerably more distant (750 --
1000 pc), and the latter has a large depth probably extending beyond 1 kpc.
Therefore, not only are the recalculated parallaxes in complete agreement with
the photometric uvbybeta parallaxes, but the structure of the field they reveal
is no longer in discrepancy with that found by the photometric method.Comment: 7 pages, 1 figure, ApJL accepte
Photometric study of two beta Cephei pulsators in eclipsing systems
We present results of a photometric study of the young southern open cluster
Stock 14. This cluster is known to contain two eclipsing systems with presumed
beta Cephei components, HD 101794 and HD 101838. We confirm variability due to
pulsations and eclipses in both targets and announce the discovery of other
variable stars in the observed field.Comment: 3 pages, 4 figures, Astronomische Nachrichten, HELAS IV Conference,
Arecife, Lanzarote, Feb 2010, submitte
Characterization and Development of Novel Stationary Phases for Capillary Electrochromatography
Porous monolithic stationary phases for capillary electrochromatography have shown great potential due to the ability to tune their properties for tailor-made separations by careful selection of the polymerization parameters. However, the final morphological and chemical properties of the column remain difficult to predict. In order to better understand the effects of the relevant variables on column properties and morphology we have significantly streamlined the preparation procedure and investigated an array of variables (temperature, reaction time, porogenic solvent concentration) on the porosity and retention of the columns. Factorial experimental design was implemented to derive models that were able to describe the polymer porosity and the retention of three PAH’s as a function of starting reagents and conditions.
The current study showed that with a factorial design approach, monolith porosity and chromatography can be reliably tuned by adjusting the porogenic solvent concentration, the polymerization time and reaction temperature. Scanning electron microscopy revealed that the polymerization conditions affected the polymer structure and particle size. Synergistic effects not accessible by the “one variable at time” approach were identified between the temperature and polymerization time and temperature and monomer/porogenic solvent ratio through multivariate analysis. The control of the monolith porosity and chromatographic behaviour will allow future efforts to be focused on creating reproducible, tailor-made monolithic columns with targeted chromatographic properties suitable for the separation of peptides and proteins from biological fluids
Astrophysical parameters of LS2883 and implications for the PSR B1259-63 gamma-ray binary
Only a few binary systems with compact objects display TeV emission. The
physical properties of the companion stars represent basic input to understand
the physical mechanisms behind the particle acceleration, emission, and
absorption processes in these so-called gamma-ray binaries. Here we present
high-resolution and high signal-to-noise optical spectra of LS2883, the Be star
forming a gamma-ray binary with the young non-accreting pulsar PSR B1259-63,
showing it to rotate faster and be significantly earlier and more luminous than
previously thought. Analysis of the interstellar lines suggest that the system
is located at the same distance as (and thus is likely a member of) CenOB1.
Taking the distance to the association, d=2.3kpc, and a color excess of
E(B-V)=0.85 for LS2883, results in Mv=-4.4. Because of fast rotation, LS2883 is
oblate (R_eq=9.7R_sun and R_pole=8.1R_sun) and presents a temperature gradient
(T_eq=27500K, log g_eq=3.7; T_pole=34000K, log g_pole=4.1). If the star did not
rotate, it would have parameters corresponding to a late O-type star. We
estimate its luminosity at log(L*/L_sun)=4.79, and its mass at M=30M_sun. The
mass function then implies an inclination of the binary system
i_orb=23deg,slightly smaller than previous estimates. We discuss the
implications of these new astrophysical parameters of LS2883 for the production
of high energy and very high energy gamma rays in the PSR B1259-63/LS2883
gamma-ray binary system. In particular, the stellar properties are very
important for prediction of the line-like bulk Comptonization component from
the unshocked ultra-relativistic pulsar wind.Comment: Accepted for publication in ApJ
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