173 research outputs found
X-ray Study of Triggered Star Formation and Protostars in IC 1396N
The IC 1396N cometary globule within the large nearby HII region IC 1396 has
been observed with the ACIS detector on board the Chandra X-ray Observatory. We
detect 117 X-ray sources, of which ~50-60 are likely members of the young open
cluster Trumpler~37 dispersed throughout the HII region, and 25 are associated
with young stars formed within the globule. Spitzer/2MASS photometry shows the
X-ray population is very young: 3 older Class III stars, 16 classical T Tauri
stars, 6 protostars including a Class 0/I system. We infer a total T Tauri
population of ~30 stars in the globule, including the undetected population,
with a star formation efficiency of 1-4%. An elongated source spatial
distribution with an age gradient oriented towards the exciting star is
discovered in the X-ray population of IC 1396N, supporting similar findings in
other cometary globules. The geometric and age distribution is consistent with
the RDI model for triggered star formation in CGs by HII region shocks. The
inferred velocity of the shock front propagating into the globule is ~0.6km/s.
The large number of X-ray-luminous protostars in the globule suggests either an
unusually high ratio of Class I/0 vs. Class II/III stars, or a non-standard IMF
favoring higher mass stars by the triggering process. The Chandra source
associated with the luminous Class 0/I protostar IRAS 21391+5802 is one of the
youngest stars ever detected in the X-ray band. We also establish for the first
time that the X-ray absorption in protostars arises from the local infalling
envelopes rather than ambient molecular cloud material.Comment: 50 pages, 11 figures, 6 tables, accepted for publication in ApJ
09/11/0
Oscillatory regime in the Multidimensional Homogeneous Cosmological Models Induced by a Vector Field
We show that in multidimensional gravity vector fields completely determine
the structure and properties of singularity. It turns out that in the presence
of a vector field the oscillatory regime exists in all spatial dimensions and
for all homogeneous models. By analyzing the Hamiltonian equations we derive
the Poincar\'e return map associated to the Kasner indexes and fix the rules
according to which the Kasner vectors rotate. In correspondence to a
4-dimensional space time, the oscillatory regime here constructed overlap the
usual Belinski-Khalatnikov-Liftshitz one.Comment: 9 pages, published on Classical and Quantum Gravit
Scans for signatures of selection in Russian cattle breed genomes reveal new candidate genes for environmental adaptation and acclimation
Domestication and selective breeding has resulted in over 1000 extant cattle breeds. Many of these breeds do not excel in important traits but are adapted to local environments. These adaptations are a valuable source of genetic material for efforts to improve commercial breeds. As a step toward this goal we identified candidate regions to be under selection in genomes of nine Russian native cattle breeds adapted to survive in harsh climates. After comparing our data to other breeds of European and Asian origins we found known and novel candidate genes that could potentially be related to domestication, economically important traits and environmental adaptations in cattle. The Russian cattle breed genomes contained regions under putative selection with genes that may be related to adaptations to harsh environments (e.g., AQP5, RAD50, and RETREG1). We found genomic signatures of selective sweeps near key genes related to economically important traits, such as the milk production (e.g., DGAT1, ABCG2), growth (e.g., XKR4), and reproduction (e.g., CSF2). Our data point to candidate genes which should be included in future studies attempting to identify genes to improve the extant breeds and facilitate generation of commercial breeds that fit better into the environments of Russia and other countries with similar climates
Cloud Structure and Physical Conditions in Star-Forming Regions from Optical Observations. II. Analysis
To complement the optical absorption-line survey of diffuse molecular gas in
Paper I, we obtained and analyzed far ultraviolet H and CO data on lines of
sight toward stars in Cep OB2 and Cep OB3. Possible correlations between column
densities of different species for individual velocity components, not total
columns along a line of sight as in the past, were examined and were
interpreted in terms of cloud structure. The analysis reveals that there are
two kinds of CH in diffuse molecular gas: CN-like CH and CH-like CH.
Evidence is provided that CO is also associated with CN in diffuse molecular
clouds. Different species are distributed according to gas density in the
diffuse molecular gas. Both calcium and potassium may be depleted onto grains
in high density gas, but with different dependences on local gas density. Gas
densities for components where CN was detected were inferred from a chemical
model. Analysis of cloud structure indicates that our data are generally
consistent with the large-scale structure suggested by maps of CO
millimeter-wave emission. On small scales, the gas density is seen to vary by
factors greater than 5.0 over scales of 10,000 AU. The relationships
between column densities of CO and CH with that of H along a line of sight
show similar slopes for the gas toward Cep OB2 and OB3, but the CO/H and
CH/H ratios tend to differ which we ascribe to variation in average density
along the line of sight.Comment: 49 pages, 9 figures, accepted by Ap
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