1,282 research outputs found
Forbidden Line Emission in the Eccentric Spectroscopic Binaries DQ Tauri and UZ Tauri E Monitored over an Orbital Period
We present echelle spectroscopy of the close pre-main-sequence binary star
systems DQ Tau and UZ Tau-E. Over a 16 day time interval we acquired 14 nights
of spectra for DQ Tau and 12 nights of spectra for UZ Tau-E. This represents
the entire phase of DQ Tau, and 63 percent of the phase of UZ Tau-E. As
expected, photospheric lines such as Li I 6707 clearly split into two
components as the primary and secondary orbit one another, as did the permitted
line He I 5876. Unlike the photospheric features, the forbidden lines of [O I]
6300 and [O I] 5577, retain the same shape throughout the orbit. Therefore
these lines must originate outside of the immediate vicinity of the two stars
and any circumstellar disks that participate in the orbital motion of the
stars.Comment: 14 pages including 6 figures, aastex preprint, accepted to
Astronomical Journa
A Survey of Irradiated Pillars, Globules, and Jets in the Carina Nebul
We present wide-field, deep narrowband H, Br, H, [S II],
[O III], and broadband I and K-band images of the Carina star formation region.
The new images provide a large-scale overview of all the H and Br
emission present in over a square degree centered on this signature star
forming complex. By comparing these images with archival HST and Spitzer images
we observe how intense UV radiation from O and B stars affects star formation
in molecular clouds. We use the images to locate new candidate outflows and
identify the principal shock waves and irradiated interfaces within dozens of
distinct areas of star-forming activity. Shocked molecular gas in jets traces
the parts of the flow that are most shielded from the intense UV radiation.
Combining the H and optical images gives a more complete view of the jets,
which are sometimes only visible in H. The Carina region hosts several
compact young clusters, and the gas within these clusters is affected by
radiation from both the cluster stars and the massive stars nearby. The Carina
Nebula is ideal for studying the physics of young H II regions and PDR's, as it
contains multiple examples of walls and irradiated pillars at various stages of
development. Some of the pillars have detached from their host molecular clouds
to form proplyds. Fluorescent H outlines the interfaces between the ionized
and molecular gas, and after removing continuum, we detect spatial offsets
between the Br and H emission along the irradiated interfaces.
These spatial offsets can be used to test current models of PDRs once synthetic
maps of these lines become available.Comment: Accepted in the Astronomical Journa
Laboratory Experiments, Numerical Simulations, and Astronomical Observations of Deflected Supersonic Jets: Application to HH 110
Collimated supersonic flows in laboratory experiments behave in a similar
manner to astrophysical jets provided that radiation, viscosity, and thermal
conductivity are unimportant in the laboratory jets, and that the experimental
and astrophysical jets share similar dimensionless parameters such as the Mach
number and the ratio of the density between the jet and the ambient medium.
Laboratory jets can be studied for a variety of initial conditions, arbitrary
viewing angles, and different times, attributes especially helpful for
interpreting astronomical images where the viewing angle and initial conditions
are fixed and the time domain is limited. Experiments are also a powerful way
to test numerical fluid codes in a parameter range where the codes must perform
well. In this paper we combine images from a series of laboratory experiments
of deflected supersonic jets with numerical simulations and new spectral
observations of an astrophysical example, the young stellar jet HH 110. The
experiments provide key insights into how deflected jets evolve in 3-D,
particularly within working surfaces where multiple subsonic shells and
filaments form, and along the interface where shocked jet material penetrates
into and destroys the obstacle along its path. The experiments also underscore
the importance of the viewing angle in determining what an observer will see.
The simulations match the experiments so well that we can use the simulated
velocity maps to compare the dynamics in the experiment with those implied by
the astronomical spectra. The experiments support a model where the observed
shock structures in HH 110 form as a result of a pulsed driving source rather
than from weak shocks that may arise in the supersonic shear layer between the
Mach disk and bow shock of the jet's working surface.Comment: Full resolution figures available at
http://sparky.rice.edu/~hartigan/pub.html To appear in Ap
Astrophysical jets: observations, numerical simulations, and laboratory experiments
This paper provides summaries of ten talks on astrophysical jets given at the HEDP/HEDLA-08 International Conference in St. Louis. The talks are topically divided into the areas of observation, numerical modeling, and laboratory experiment. One essential feature of jets, namely, their filamentary (i.e., collimated) nature, can be reproduced in both numerical models and laboratory experiments. Another essential feature of jets, their scalability, is evident from the large number of astrophysical situations where jets occur. This scalability is the reason why laboratory experiments simulating jets are possible and why the same theoretical models can be used for both observed astrophysical jets and laboratory simulations
On the structure and stability of magnetic tower jets
Modern theoretical models of astrophysical jets combine accretion, rotation,
and magnetic fields to launch and collimate supersonic flows from a central
source. Near the source, magnetic field strengths must be large enough to
collimate the jet requiring that the Poynting flux exceeds the kinetic-energy
flux. The extent to which the Poynting flux dominates kinetic energy flux at
large distances from the engine distinguishes two classes of models. In
magneto-centrifugal launch (MCL) models, magnetic fields dominate only at
scales engine radii, after which the jets become
hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD)
magnetic tower models, the field dominates even out to much larger scales. To
compare the large distance propagation differences of these two paradigms, we
perform 3-D ideal MHD AMR simulations of both HD and PFD stellar jets formed
via the same energy flux. We also compare how thermal energy losses and
rotation of the jet base affects the stability in these jets. For the
conditions described, we show that PFD and HD exhibit observationally
distinguishable features: PFD jets are lighter, slower, and less stable than HD
jets. Unlike HD jets, PFD jets develop current-driven instabilities that are
exacerbated as cooling and rotation increase, resulting in jets that are
clumpier than those in the HD limit. Our PFD jet simulations also resemble the
magnetic towers that have been recently created in laboratory astrophysical jet
experiments.Comment: 16 pages, 11 figures, published in ApJ: ApJ, 757, 6
Chandra observation of Cepheus A: The diffuse emission of HH 168 resolved
X-ray emission from massive stellar outflows has been detected in several
cases. We present a Chandra observation of HH 168 and show that the soft X-ray
emission from a plasma of 0.55 keV within HH 168 is diffuse. The X-ray emission
is observed on two different scales: Three individual, yet extended, regions
are embedded within a complex of low X-ray surface brightness. Compared to the
bow shock the emission is displaced against the outflow direction. We show that
there is no significant contribution from young stellar objects (YSOs) and
discuss several shock scenarios that can produce the observed signatures. We
establish that the X-ray emission of HH 168 is excited by internal shocks in
contrast to simple models, which expect the bow shock to be the most X-ray
luminous.Comment: 8 pages, 5 figures, accepted for publication in A&
Unveiling extremely veiled T Tauri stars
Photospheric absorption lines in classical T Tauri stars (CTTS) are weak
compared to normal stars. This so-called veiling is normally identified with an
excess continuous emission formed in shock-heated gas at the stellar surface
below the accretion streams. We have selected four stars (RW Aur A, RU Lup, S
CrA NW and S CrA SE) with unusually strong veiling to make a detailed
investigation of veiling versus stellar brightness and emission line strengths
for comparisons to standard accretion models. We have monitored the stars
photometrically and spectroscopically at several epochs. In standard accretion
models a variable accretion rate will lead to a variable excess emission.
Consequently, the stellar brightness should vary accordingly. We find that the
veiling of absorption lines in these stars is strongly variable and usually so
large that it would require the release of several stellar luminosities of
potential energy. At states of very large line dilution, the correspondingly
large veiling factors derived correlate only weakly with brightness. Moreover,
the emission line strengths violate the expected trend of veiling versus line
strength. The veiling can change dramatically in one night, and is not
correlated with the phase of the rotation periods found for two stars. We show
that in at least three of the stars, when the veiling becomes high, the
photospheric lines become filled-in by line emission, which produces large
veiling factors unrelated to changes in any continuous emission from shocked
regions. We also consider to what extent extinction by dust and electron
scattering in the accretion stream may affect veiling measures in CTTS. We
conclude that the degree of veiling cannot be used as a measure of accretion
rates in CTTS with rich emission line spectra.Comment: Accepted for publication in A&A Letters. New language-edited version.
(4 pages, 3 figures
Jets and Outflows From Star to Cloud: Observations Confront Theory
In this review we focus on the role jets and outflows play in the star and
planet formation process. Our essential question can be posed as follows: are
jets/outflows merely an epiphenomenon associated with star formation or do they
play an important role in mediating the physics of assembling stars both
individually and globally? We address this question by reviewing the current
state of observations and their key points of contact with theory. Our review
of jet/outflow phenomena is organized into three length-scale domains: Source
and Disk Scales ( au) where the connection with protostellar and disk
evolution theories is paramount; Envelope Scales ( au) where the
chemistry and propagation shed further light on the jet launching process, its
variability and its impact on the infalling envelope; Parent Cloud Scales
( au) where global momentum injection into cluster/cloud
environments become relevant. Issues of feedback are of particular importance
on the smallest scales where planet formation regions in a disk may be impacted
by the presence of disk winds, irradiation by jet shocks or shielding by the
winds. Feedback on envelope scales may determine the final stellar mass
(core-to-star efficiency) and envelope dissipation. Feedback also plays an
important role on the larger scales with outflows contributing to turbulent
support within clusters including alteration of cluster star formation
efficiencies (feedback on larger scales currently appears unlikely). A
particularly novel dimension of our review is that we consider results on jet
dynamics from the emerging field of High Energy Density Laboratory Astrophysics
(HEDLA). HEDLA is now providing direct insights into the 3-D dynamics of fully
magnetized, hypersonic, radiative outflows.Comment: Accepted for publication as a chapter in Protostars and Planets VI,
University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C.
Dullemond, Th. Hennin
Star Spot Induced Radial Velocity Variability in LkCa 19
We describe a new radial velocity survey of T Tauri stars and present the
first results. Our search is motivated by an interest in detecting massive
young planets, as well as investigating the origin of the brown dwarf desert.
As part of this survey, we discovered large-amplitude, periodic, radial
velocity variations in the spectrum of the weak line T Tauri star LkCa 19.
Using line bisector analysis and a new simulation of the effect of star spots
on the photometric and radial velocity variability of T Tauri stars, we show
that our measured radial velocities for LkCa19 are fully consistent with
variations caused by the presence of large star spots on this rapidly rotating
young star. These results illustrate the level of activity-induced radial
velocity noise associated with at least some very young stars. This
activity-induced noise will set lower limits on the mass of a companion
detectable around LkCa 19, and similarly active young stars.Comment: ApJ accepted, 27 pages, 12 figures, aaste
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