27,905 research outputs found
Masers in star forming regions
Maser emission plays an important role as a tool in star formation studies.
It is widely used for deriving kinematics, as well as the physical conditions
of different structures, hidden in the dense environment very close to the
young stars, for example associated with the onset of jets and outflows. We
will summarize the recent observational and theoretical progress on this topic
since the last maser symposium: the IAU Symposium 242 in Alice Springs.Comment: Submitted to Proceedings of IAU Symposium No. 287, Cosmic masers -
from OH to H
Star-Forming Regions near GRB 990123
We reduced the Hubble Space Telescope Space Telescope Imaging Spectrograph
images of the gamma-ray burst GRB 990123 that were obtained on 8-9 February
1999 and find V_0 = 25.36 +/- 0.10, which corresponds to a flux of 0.258 +/-
0.023 micro-Jy for the optical transient 16.644 days after the burst's peak.
The probable host galaxy has V_0 = 24.25 +/- 0.07 (= 0.716 +/- 0.046 micro-Jy)
and the optical transient is located 0.65 arcseconds (= 5.5 kpc) south of the
galaxy's nucleus. We fit and subtracted a scaled point-spread function to the
optical transient and found evidence for three bright knots situated within 0.5
arcseconds (= 4.3 kpc) of the optical transient. Each knot has V_0 ~ 28.1 +/-
0.3, a rest-frame V-band luminosity of between approximately 5e8 L_Sun and 8e8
L_Sun, and a star-formation rate of at least 0.1-0.2 Solar masses per year. The
knots are centrally concentrated with full-width at half-maximum of
approximately 0.17 arcseconds (= 1.5 kpc). Their sizes and luminosities are
consistent with their being star-forming regions. The optical transient is
located 0.15 arcseconds (= 1.3 kpc) southeast of the centre of one of these
knots.Comment: 4 pages, 2 figures, to appear in Astronomy & Astrophysics Letter
Age spreads in star forming regions?
Rotation periods and projected equatorial velocities of pre-main-sequence
(PMS) stars in star forming regions can be combined to give projected stellar
radii. Assuming random axial orientation, a Monte-Carlo model is used to
illustrate that distributions of projected stellar radii are very sensitive to
ages and age dispersions between 1 and 10 Myr which, unlike age estimates from
conventional Hertzsprung-Russell diagrams, are relatively immune to
uncertainties due to extinction, variability, distance etc. Application of the
technique to the Orion Nebula cluster reveals radius spreads of a factor of
2--3 (FWHM) at a given effective temperature. Modelling this dispersion as an
age spread suggests that PMS stars in the ONC have an age range larger than the
mean cluster age, that could be reasonably described by the age distribution
deduced from the Hertzsprung-Russell diagram. These radius/age spreads are
certainly large enough to invalidate the assumption of coevality when
considering the evolution of PMS properties (rotation, disks etc.) from one
young cluster to another.Comment: To appear in "The Ages of Stars", E.E. Mamajek, D.R. Soderblom,
R.F.G. Wyse (eds.), IAU Symposium 258, CU
Deuterated species in extragalactic star-forming regions
We present a theoretical study of the deuterated species detectability in
various types of extragalactic star-forming regions based on our predictions of
chemical abundances. This work is motivated by the past and current attempts at
observing deuterated species in external galaxies such as NGC~253, IC~342 and
the LMC. Here, we investigate the influence of the density, the temperature,
the FUV radiation field, the cosmic ray ionisation, and the metallicity on the
fractional abundances and D/H abundance ratios of about 20 deuterated species.
Without modelling any particular source, we determined how the deuterium
chemistry behaves in different physical environments such as starburst,
cosmic-rays enhanced environments, low metallicity and high redshift galaxies.
In general, our predicted column densities seem in good agreement with those
derived from the current limited dataset of observations in external galaxies.
We provide, for the first time, a list of key deuterated species whose
abundances are high enough to be possibly detectable by the Atacama Large
Millimeter Array (ALMA) and Herschel, as a function of galactic nuclear
activity and redshift.Comment: 19 pages, 6 figures, 5 tables, In press in Ap
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