2,255 research outputs found
Multiwavelength Observations of Young Stars and Their Circumstellar Disks
Observational studies of star and planet formation represent a fundamental means to understand the origins of exoplanetary systems and our own solar system. In this dissertation I present a multiwavelength approach to study a wide range of stages of the evolution of protostars and pre-main sequence (pre-MS) stars. I have investigated, via an infrared and multi-epoch X-ray study of the L1630 dark cloud, whether and how X-ray variability in young stellar objects is related to protostellar evolutionary state. Among a subsample of 52 X-ray-emitting young stars in L1630, I find that the earliest stages of young stellar evolution show the highest levels of X-ray variability, indicative of high levels of magnetic activity during star formation. I also find evidence of active magnetospheric accretion in three L1630 stars with circumstellar disks.
I also present multiwavelength analyses of several phenomenologically interesting young stars at different stages of pre-MS stellar evolution. I investigate, via contemporaneous X-ray and optical/IR observations, the nearby, pre-main sequence star/disk systems T Chamaeleontis (T Cha) and TWA 30A and 30B. I analyze X-ray and optical emission signatures of accretion and magnetic activity in T Cha, and infer the X-ray absorbing properties of its circumstellar disk. Like T Cha, each component of the wide binary TWA 30A and 30B is viewed through a highly inclined circumstellar disk. Both TWA 30A and 30B display large near-IR variability, suggestive of (respectively) variable obscuration of the stellar photosphere and a possible disk-rim warp. In the case of T Cha and TWA 30A, I find a correlation of optical/near-IR and X-ray extinction consistent with that of photospheric obscuration from an intervening disk clump
Evidence for Variable, Correlated X-ray and Optical/IR Extinction toward the Nearby, Pre-main Sequence Binary TWA 30
We present contemporaneous XMM-Newton X-ray and ground-based optical/near-IR
spectroscopic observations of the nearby ( pc), low-mass (mid-M)
binary system TWA 30A and 30B. The components of this wide (separation
3400 AU) binary are notable for their nearly edge-on disk viewing
geometries, high levels of variability, and evidence for collimated stellar
outflows. We obtained XMM-Newton X-ray observations of TWA 30A and 30B in 2011
June and July, accompanied (respectively) by IRTF SpeX (near-IR) and VLT
XSHOOTER (visible/near-IR) spectroscopy obtained within 20 hours of the
X-ray observations. TWA 30A was detected in both XMM-Newton observations at
relatively faint intrinsic X-ray luminosities (
) compared to stars of similar mass and age . The intrinsic
(0.15-2.0 keV) X-ray luminosities measured in 2011 had decreased by a factor
20-100 relative to a 1990 (ROSAT) X-ray detection. TWA 30B was not detected,
and we infer an upper limit of ( 3.0 erg
s). We measured a large change in visual extinction toward TWA 30A (from
to ) between the two 2011 observing epochs,
and we find evidence for a corresponding significant decrease in X-ray
absorbing column (). The apparent correlated change in and is
suggestive of variable obscuration of the stellar photosphere by disk material
composed of both gas and dust. However, in both observations, the inferred
to ratio is lower than that typical of the ISM, suggesting that
the disk is either depleted of gas or is deficient in metals in the gas phase.Comment: 10 pages, 7 figures, Accepted for publication in MNRA
The ALMA Early Science View of FUor/EXor objects. III. The Slow and Wide Outflow of V883 Ori
We present Atacama Large Millimeter/ sub-millimeter Array (ALMA) observations
of V883 Ori, an FU Ori object. We describe the molecular outflow and envelope
of the system based on the CO and CO emissions, which together
trace a bipolar molecular outflow. The CO emission traces the rotational
motion of the circumstellar disk. From the CO blue-shifted emission, we
estimate a wide opening angle of 150 for the outflow
cavities. Also, we find that the outflow is very slow (characteristic velocity
of only 0.65 km~s), which is unique for an FU Ori object. We calculate
the kinematic properties of the outflow in the standard manner using the
CO and CO emissions. In addition, we present a P Cygni profile
observed in the high-resolution optical spectrum, evidence of a wind driven by
the accretion and being the cause for the particular morphology of the
outflows. We discuss the implications of our findings and the rise of these
slow outflows during and/or after the formation of a rotationally supported
disk.Comment: 12 pages, 7 figures, 2 tables. Accepte
Nearby Young Stars and Young Moving Groups
The past two decades have seen dramatic progress in our knowledge of the
population of stars of age 150 Myr that lie within 100 pc of
the Sun. Most such stars are found in loose kinematic groups ("nearby young
moving groups"; NYMGs). The proximity of NYMGs and their members facilitates
studies of the X-ray properties of coeval groups of pre-main sequence (pre-MS)
stars as well as of individual pre-MS systems. In this review, we focus on how
NYMG X-ray studies provide unique insight into the early evolution of stellar
magnetic activity, the X-ray signatures of accretion, and the irradiation and
dissipation of protoplanetary disks by high-energy photons originating with
their host pre-MS stars. We discuss the likely impacts of the next generation
of X-ray observing facilities on these aspects of the study of NYMGs and their
members.Comment: To appear in Springer's "Handbook of X-ray and Gamma-ray
Astrophysics" (eds. A. Santangelo and C. Bambi), Section "The Sun, Stars &
Planets" (eds. G. Micela & B. Stelzer
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