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: $M_J[(J-K)_0]$. 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 $n_H\sim A_{V,\star}/D_\star$ 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$\alpha$, $^{12}$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 $299^\circ \le l \le 311^\circ$ and $-5^\circ \le b \le 7^\circ$. The investigation is based on nearly 700 O-B9 stars with $uvby\beta$ 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 1.8$\pm$0.4 (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