* Astronomy

Blobrana · L

RE: Trumpler 16

Blobrana · L

Title: The Search for Low-mass Companions of B Stars in the Carina Nebula Cluster Trumpler 16
Authors: Nancy Remage Evans, Kathleen DeGioia-Eastwood, Marc Gagne, Leisa Townsley, Patrick Broos, Scott Wolk, Yael Naze, Michael Corcoran, Lida Oskinova, Anthony F. J. Moffat, Junfeng Wang, Nolan R. Walborn

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). Colour and magnitude cuts have been made assuming an E(B-V) =0.55 mag ±0.1, which is a good approximation close to the centre 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.

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Blobrana · L

Hubble captures views of mammoth stars
Two of our galaxy's most massive stars, until recently shrouded in mystery, have been viewed by the NASA/ESA Hubble Space Telescope, unveiling greater detail than ever before.
The image shows a pair of colossal stars, WR 25 and Tr16-244, located within the open cluster Trumpler 16. This cluster is embedded within the Carina Nebula, an immense cauldron of gas and dust that lies approximately 7500 light-years from Earth. The Carina Nebula contains several ultra-hot stars, including these two star systems and the famous blue star Eta Carinae, which has the highest luminosity yet confirmed.
These stars are very bright and they produce incredible amounts of heat, emitting most of their radiation in the ultraviolet and appearing blue in colour. They are so powerful that they burn through their hydrogen fuel source faster than other types of stars, leading to a live fast, die young stellar lifestyle.

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Blobrana · L

Title: An X-ray survey of low-mass stars in Trumpler 16 with Chandra
Authors: J.F. Albacete-Colombo, F. Damiani, G. Micela, S. Sciortino, F.R. Harnden Jr

We identify and characterise low-mass stars in the ~3 Myr old Trumpler 16 (Tr16) region by means of a deep Chandra X-ray observation, and study their optical and near-IR properties. We compare X-ray activity of Tr16 stars with known characteristics of Orion and Cygnus OB2 stars. We analysed a 88.4 ksec Chandra ACIS-I observation pointed at the centre of Tr16. Because of diffuse X-ray emission, source detection was performed using the PWDetect code for two different energy ranges: 0.5-8.0 keV and 0.9-8.0 keV. Results were merged into a single final list. We positionally correlate X-ray sources with optical and 2MASS catalogues. Source events were extracted with the IDL-based routine ACIS-Extract. X-ray variability was characterised using the Kolmogorov-Smirnov test and spectra were fitted by using XSPEC. X-ray spectra of early-type, massive stars were analysed individually. Our list of X-ray sources consists of 1035 entries, 660 of which have near-IR counterparts and are probably associated with Tr16 members. From near-IR colour-colour and colour-magnitudes diagrams we compute individual masses of stars and their Av values. About 15% of the near-IR counterparts show disk-induced excesses. X-ray variability is found in 77 sources. X-ray emission from OB stars appear softer than the low-mass stars. The Tr16 region has a very rich population of low-mass X-ray emitting stars. An important fraction of its circumstellar disks survive the intense radiation field of its massive stars. Stars with masses 1.5-2.5 Mo display X-ray activity similar to that of stars in Cyg OB2 but much less intense than observed for Orion Nebula Cluster members.

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