14 research outputs found
Kinematics of the Young Stellar Objects associated with the Cometary Globules in the Gum Nebula
An analysis of proper motion measurements of the Young Stellar Objects (YSOs)
associated with the Cometary Globules (CGs) in the Gum Nebula is presented.
While earlier studies based on the radial velocity measurements of the CGs
suggested expansion of the system of the CGs, the observed proper motion of the
YSOs shows no evidence for expansion. In particular the kinematics of two YSOs
embedded in CGs is inconsistent with the supernova explosion of the companion
of Pup about 1.5 Myr ago as the cause of the expansion of the CG
system. YSOs associated with the CGs share the average proper motion of the
member stars of the Vela OB2 association. A few YSOs that have relatively large
proper motions are found to show relatively low infrared excesses.Comment: 19 pages, 6 figures, 4 tables, Accepted for publication in MNRA
Detection of an ultra-bright submillimeter galaxy in the Subaru/XMM-Newton Deep Field using AzTEC/ASTE
We report the detection of an extremely bright (37 mJy at 1100 m
and 91 mJy at 880 m) submillimeter galaxy (SMG),
AzTEC-ASTE-SXDF1100.001 (hereafter referred to as SXDF1100.001 or Orochi),
discovered in 1100 m observations of the Subaru/XMM-Newton Deep Field
using AzTEC on ASTE. Subsequent CARMA 1300 m and SMA 880 m
observations successfully pinpoint the location of Orochi and suggest that it
has two components, one extended (FWHM of 4) and one
compact (unresolved). Z-Spec on CSO has also been used to obtain a wide band
spectrum from 190 to 308 GHz, although no significant emission/absorption lines
are found. The derived upper limit to the line-to-continuum flux ratio is
0.1--0.3 (2 ) across the Z-Spec band.
Based on the analysis of the derived spectral energy distribution from
optical to radio wavelengths of possible counterparts near the SMA/CARMA peak
position, we suggest that Orochi is a lensed, optically dark SMG lying at behind a foreground, optically visible (but red) galaxy at . The deduced apparent (i.e., no correction for magnification) infrared
luminosity () and star formation rate (SFR) are
and 11000 yr, respectively, assuming that the
is dominated by star formation. These values suggest that Orochi
will consume its gas reservoir within a short time scale (
yr), which is indeed comparable to those in extreme starbursts like the centres
of local ULIRGs.Comment: 18 pages, 13 figure
Early-Age Evolution of the Milky Way Related by Extremely Metal-Poor Stars
We exploit the recent observations of extremely metal-poor (EMP) stars in the
Galactic halo and investigate the constraints on the IMF of the stellar
population that left these low-mass survivors of [Fe/H]<-2.5 and the chemical
evolution that they took part in. A high-mass IMF with the typical mass~10Msun
and the overwhelming contribution of low-mass members of binaries to the EMP
survivors are derived from the statistics of carbon-enriched EMP stars with and
without the enhancement of s-process elements (Komiya et al. 2007). We first
examine the analysis to confirm their results for various assumptions on the
mass-ratio distribution function. As compared with the uniform distribution,
the increase or decrease function of the mass ratio gives a higher- or
lower-mass IMF, and a lower-mass IMF results for the independent distribution
with the both members in the same IMF, but the derived ranges of typical mass
differ less than by a factor of two and overlap for the extreme cases.
Furthermore, we prove that the same constraints are placed on the IMF from the
surface density of EMP stars estimated from the surveys and the chemical
evolution consistent with the metal yields of theoretical supernova models. We
then apply the derived high-mass IMF with the binary contribution to show that
the observed MDF of EMP stars can be reproduced not only for the shape but also
for the number of EMP stars. In particular, the scarcity of stars below
[Fe/H]<-4 is naturally explained in terms of the hierarchical structure
formation, and there is no indication of significant changes in the IMF for the
EMP Population. The present study indicates that 3 HMP stars of [Fe/H]<-4 are
the primordial stars that were born as the low-mass members of binaries before
the host clouds were polluted by their own supernovae.Comment: 19 pages, 9 figures, accepted in Ap
Zeta Oph and the weak-wind problem
Mass-loss rate, , is one of the key parameters affecting evolution
and observational manifestations of massive stars, and their impact on the
ambient medium. Despite its importance, there is a factor of ~100 discrepancy
between empirical and theoretical of late-type O dwarfs, the
so-called weak-wind problem. In this Letter, we propose a simple novel method
to constrain of runaway massive stars through observation of their
bow shocks and Stromgren spheres, which might be of decisive importance for
resolving the weak-wind problem. Using this method, we found that of
the well-known runaway O9.5 V star zeta Oph is more than an order of magnitude
higher than that derived from ultraviolet (UV) line-fitting (Marcolino et al.
2009) and is by a factor of 6 to 7 lower than those based on the theoretical
recipe by Vink et al. (2000) and the Halpha line (Mokiem et al. 2005). The
discrepancy between derived by our method and that based on UV lines
would be even more severe if the stellar wind is clumpy. At the same time, our
estimate of agrees with that predicted by the moving reversing layer
theory by Lucy (2010).Comment: 5 pages, 1 figure, 2 tables. Accepted for publication in MNRAS
Letter