Multi-color pyrometer for materials processing in space

The design, construction and calibration of a computer-linked multicolor pyrometer is described. The device was constructed for ready adaptation to a spacecraft and for use in the control of thermal processes for manufacturing materials in space. The pyrometer actually uses only one color at a time, and is relatively insensitive to uncertainties in the heated object's emissivity because the product of the color and the temperature has been selected to be within a regime where the radiant energy emitted from the body increases very rapidly with temperature. The instrument was calibrated and shown to exceed its design goal of temperature measurements between 300 and 2000 C, and its accuracy in the face of imprecise knowledge of the hot object's emissivity was demonstrated

Seasonal Genetic Influence on Serum 25-Hydroxyvitamin D Levels: A Twin Study

Although environmental factors, mainly nutrition and UV-B radiation, have been considered major determinants of vitamin D status, they have only explained a modest proportion of the variation in serum 25-hydroxyvitamin D. We aimed to study the seasonal impact of genetic factors on serum 25-hydroxyvitamin D concentrations.204 same-sex twins, aged 39-85 years and living at northern latitude 60 degrees, were recruited from the Swedish Twin Registry. Serum 25-hydroxyvitamin D was analysed by high-pressure liquid chromatography and mass spectrometry. Genetic modelling techniques estimated the relative contributions of genetic, shared and individual-specific environmental factors to the variation in serum vitamin D. The average serum 25-hydroxyvitamin D concentration was 84.8 nmol/l (95% CI 81.0-88.6) but the seasonal variation was substantial, with 24.2 nmol/l (95% CI 16.3-32.2) lower values during the winter as compared to the summer season. Half of the variability in 25-hydroxyvitamin D during the summer season was attributed to genetic factors. In contrast, the winter season variation was largely attributable to shared environmental influences (72%; 95% CI 48-86%), i.e., solar altitude. Individual-specific environmental influences were found to explain one fourth of the variation in serum 25-hydroxyvitamin D independent of season.There exists a moderate genetic impact on serum vitamin D status during the summer season, probably through the skin synthesis of vitamin D. Further studies are warranted to identify the genes impacting on vitamin D status

Polaris: Mass and Multiplicity

Polaris, the nearest and brightest classical Cepheid, is a member of at least a triple system. It has a wide ($18''$) physical companion, the F-type dwarf Polaris B. Polaris itself is a single-lined spectroscopic binary with an orbital period of 30 years (Kamper, 1996, JRASC, 90, 140). By combining {\it Hipparcos} measurements of the instantaneous proper motion with long-term measurements and the Kamper radial-velocity orbit, Wielen et al. (2000, A&A, 360, 399) have predicted the astrometric orbit of the close companion. Using the {\it Hubble Space Telescope} and the Advanced Camera for Surveys' High-Resolution Channel with an ultraviolet (F220W) filter, we have now directly detected the close companion. Based on the Wielen et al. orbit, the {\it Hipparcos} parallax, and our measurement of the separation ($0.176''$ $\pm$ $0.002''$), we find a preliminary mass of 5.0 $\pm$ 1.5 M$_{\odot}$ for the Cepheid and 1.38 $\pm$ 0.61 M$_{\odot}$ for the close companion. These values will be refined by additional {\it HST} observations scheduled for the next 3 years. We have also obtained a {\it Chandra} ACIS-I image of the Polaris field. Two distant companions C and D are not X-rays sources and hence are not young enough to be physical companions of the Cepheid. There is one additional stellar X-ray source in the field, located $253''$ from Polaris A, which is a possible companion. Further investigation of such a distant companion is valuable to confirm the full extent of the system.Comment: submitted to Conference Proceedings of IAU Symp. 24

Star Formation in the Era of the Three Great Observatories

This paper summarizes contributions and suggestions as presented at the Chandra Workshop Star Formation in the Era of Three Great Observatories conducted in July 2005. One of the declared goals of the workshop was to raise recognition within the star formation research community about the sensible future utilization of the space observatories Spitzer, Hubble, and Chandra in their remaining years of operation to tackle imminent questions of our understanding of stellar formation and the early evolution of stars. A white paper was generated to support the continuous and simultaneous usage of observatory time for star formation research. The contents of this paper have been presented and discussed at several other meetings during the course of 2005 and January 2006.Comment: Conference Summary "White Paper", Accepted by PASP, 9 pages including 3 figure

The Search for Low-mass Companions of B Stars in the Carina Nebula Cluster Trumpler 16

We have developed lists of likely B3--A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of Eta Car, an appropriate V and B-V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B-V) =0.55 mag +/- 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project (CCCP). Previous studies have shown that only very rarely (if at all) do late main sequence B stars produce X-rays. We present evidence that the X-ray detected sources are binaries with low-mass companions, since stars less massive than 1.4 Msun are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate mass stars are complementary to spectroscopic and interferometric results, and probe new parameter space of low mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 Msun) primaries, such as would be found by random pairing from the Initial Mass Function.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special Issue papers are available at http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at leas

X-Atlas: An Online Archive of Chandra's Stellar High Energy Transmission Gratings Observations

The high-resolution X-ray spectroscopy made possible by the 1999 deployment of the Chandra X-ray Observatory has revolutionized our understanding of stellar X-ray emission. Many puzzles remain, though, particularly regarding the mechanisms of X-ray emission from OB stars. Although numerous individual stars have been observed in high-resolution, realizing the full scientific potential of these observations will necessitate studying the high-resolution Chandra dataset as a whole. To facilitate the rapid comparison and characterization of stellar spectra, we have compiled a uniformly processed database of all stars observed with the Chandra High Energy Transmission Grating (HETG). This database, known as X-Atlas, is accessible through a web interface with searching, data retrieval, and interactive plotting capabilities. For each target, X-Atlas also features predictions of the low-resolution ACIS spectra convolved from the HETG data for comparison with stellar sources in archival ACIS images. Preliminary analyses of the hardness ratios, quantiles, and spectral fits derived from the predicted ACIS spectra reveal systematic differences between the high-mass and low-mass stars in the atlas and offer evidence for at least two distinct classes of high-mass stars. A high degree of X-ray variability is also seen in both high and low-mass stars, including Capella, long thought to exhibit minimal variability. X-Atlas contains over 130 observations of approximately 25 high-mass stars and 40 low-mass stars and will be updated as additional stellar HETG observations become public. The atlas has recently expanded to non-stellar point sources, and Low Energy Transmission Grating (LETG) observations are currently being added as well