2,821 research outputs found
Spitzer observations of Bow Shocks and Outflows in RCW 38
We report Spitzer observations of five newly identified bow shocks in the
massive star-forming region RCW 38. Four are visible at IRAC wavelengths, the
fifth is visible only at 24 microns. Chandra X-ray emission indicates that
winds from the central O5.5 binary, IRS~2, have caused an outflow to the NE and
SW of the central subcluster. The southern lobe of hot ionised gas is detected
in X-rays; shocked gas and heated dust from the shock-front are detected with
Spitzer at 4.5 and 24 microns. The northern outflow may have initiated the
present generation of star formation, based on the filamentary distribution of
the protostars in the central subcluster. Further, the bow-shock driving star,
YSO 129, is photo-evaporating a pillar of gas and dust. No point sources are
identified within this pillar at near- to mid-IR wavelengths.
We also report on IRAC 3.6 & 5.8 micron observations of the cluster
DBS2003-124, NE of RCW 38, where 33 candidate YSOs are identified. One star
associated with the cluster drives a parsec-scale jet. Two candidate HH objects
associated with the jet are visible at IRAC and MIPS wavelengths. The jet
extends over a distance of ~3 pc. Assuming a velocity of 100 km/s for the jet
material gives an age of about 30,000 years, indicating that the star (and
cluster) are likely to be very young, with a similar or possibly younger age
than RCW 38, and that star formation is ongoing in the extended RCW 38 region.Comment: 27 pages, 6 figures, accepted to Ap
XMM-Newton imaging of V1818 Ori: a young stellar group on the eastern edge of the Kappa Ori ring
We present the results of a 40 ks XMM-Newton observation centered on the
variable star V1818 Ori. Using a combination of the XMM-Newton and AllWISE
catalog data, we identify a group of about 31 young stellar objects around
V1818 Ori. This group is coincident with the eastern edge of the dust ring
surrounding Kappa Ori. Previously, we concluded that the young stellar objects
on the western side of ring were formed in an episode of star formation that
started 3-5 Myr ago, and are at a distance similar to that of kappa Ori
(250-280 pc) and in the foreground to the Orion A cloud. Here we use the
XMM-Newton observation to calculate X-ray fluxes and luminosities of the young
stars around V1818 Ori. We find that their X-ray luminosity function (XLF),
calculated for a distance of ~270 pc, matches the XLF of the YSOs west of Kappa
Ori. We rule out that this group of young stars is associated to Mon R2 as
assumed in the literature, but rather they are part of the same Kappa Ori's
ring stellar population.Comment: 4 pages, 4 figures, 1 table. Accepted for publication to A&
Near-infrared Variability among YSOs in the Star Formation Region Cygnus OB7
We present an analysis of near-infrared time-series photometry in J, H, and K
bands for about 100 epochs of a 1 square degree region of the Lynds 1003/1004
dark cloud in the Cygnus OB7 region. Augmented by data from the Wide-field
Infrared Survey Explorer (WISE), we identify 96 candidate disk bearing young
stellar objects (YSOs) in the region. Of these, 30 are clearly Class I or
earlier. Using the Wide-Field imaging CAMera (WFCAM) on the United Kingdom
InfraRed Telescope (UKIRT), we were able to obtain photometry over three
observing seasons, with photometric uncertainty better than 0.05 mag down to J
~17. We study detailed light curves and color trajectories of ~50 of the YSOs
in the monitored field. We investigate the variability and periodicity of the
YSOs and find the data are consistent with all YSOs being variable in these
wavelengths on time scales of a few years. We divide the variability into four
observational classes: 1) stars with periodic variability stable over long
timescales, 2) variables which exhibit short-lived cyclic behavior, 3) long
duration variables, and 4) stochastic variables. Some YSO variability defies
simple classification. We can explain much of the observed variability as being
due to dynamic and rotational changes in the disk, including an asymmetric or
changing blocking fraction, changes to the inner disk hole size, as well as
changes to the accretion rate. Overall, we find that the Class I:Class II ratio
of the cluster is consistent with an age of < 1Myr, with at least one
individual, wildly varying, source ~ 100,000 yr old. We have also discovered a
Class II eclipsing binary system with a period of 17.87 days.Comment: ApJ accepted: 44 pages includes 5 tables and 16 figures. Some figures
condensed for Astro/p
Transit observations of the Hot Jupiter HD 189733b at X-ray wavelengths
We present new X-ray observations obtained with Chandra ACIS-S of the HD
189733 system, consisting of a K-type star orbited by a transiting Hot Jupiter
and an M-type stellar companion. We report a detection of the planetary transit
in soft X-rays with a significantly larger transit depth than observed in the
optical. The X-ray data favor a transit depth of 6-8%, versus a broadband
optical transit depth of 2.41%. While we are able to exclude several possible
stellar origins for this deep transit, additional observations will be
necessary to fully exclude the possibility that coronal inhomogeneities
influence the result. From the available data, we interpret the deep X-ray
transit to be caused by a thin outer planetary atmosphere which is transparent
at optical wavelengths, but dense enough to be opaque to X-rays. The X-ray
radius appears to be larger than the radius observed at far-UV wavelengths,
most likely due to high temperatures in the outer atmosphere at which hydrogen
is mostly ionized. We furthermore detect the stellar companion HD 189733B in
X-rays for the first time with an X-ray luminosity of log LX = 26.67 erg/s. We
show that the magnetic activity level of the companion is at odds with the
activity level observed for the planet-hosting primary. The discrepancy may be
caused by tidal interaction between the Hot Jupiter and its host star.Comment: 15 pages, accepted for publication in The Astrophysical Journa
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