1,656 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
Observations of accretion and angular momentum regulation in young circumstellar disks and the implications for planetary formation
Accretion disks around young stars produce excess infrared continuum associated with the disk and excess optical and ultraviolet continua associated with the boundary layer or 'hot spot' as material falls from the disk onto the stellar photosphere. When we subtract the excess continuum and photospheric contributions to the total spectrum, we can obtain high-quality emission line profiles of the Balmer lines as well as permitted lines from other elements. These emission lines often exhibit redshifted absorption, indicative of infalling material. Remarkably, objects with large accretion rates tend to rotate slower than their counterparts that lack accretion disks. Hence, there must be some process, probably involving magnetic fields, that allows the star to accrete large amounts of material from the disk without increasing its rotational velocity. Young stars typically do not have optically thick inner disks that do not accrete. Hence, either planets form within accretion disks, or the timescale for planetary formation is considerably shorter than approx. 3 x 10(exp 6) yr, the duration of the classical T Tauri star phase of young stellar evolution
Simulating Radiative Magnetohydrodynamical Flows with AstroBEAR: Implementation and Applications of Non-equilibrium Cooling
Radiative cooling plays a crucial role in the dynamics of many astrophysical
flows, and is particularly important in the dense shocked gas within
Herbig-Haro (HH) objects and stellar jets. Simulating cooling processes
accurately is necessary to compare numerical simulations with existing and
planned observations of HH objects, such as those from the Hubble Space
Telescope and the James Webb Space Telescope. In this paper we discuss a new,
non-equilibrium cooling scheme we have implemented into the 3-D
magnetohydrodynamic (MHD) code AstroBEAR. The new cooling function includes
ionization, recombination, and excitation of all the important atomic species
that cool below 10000 K. We tested the routine by comparing its predictions
with those from the well-tested 1-D Cox-Raymond shock code (Raymond 1979). The
results show thatAstroBEAR accurately tracks the ionization fraction,
temperature, and other MHD variables for all low-velocity (.90 km/s) magnetized
radiative shock waves. The new routine allows us to predict synthetic emission
maps in all the bright forbidden and permitted lines observed in stellar jets,
including H{\alpha}, [NII], [OI], and [SII]. We present an example as to how
these synthetic maps facilitate a direct comparison with narrowband images of
HH objects.Comment: 8 figure
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