46 research outputs found
An Adaptive Optics Survey for Close Protostellar Binaries
In order to test the hypothesis that Class I protostellar binary stars are a
product of ejections during the dynamical decay of non-hierarchical multiple
systems, we combined the results of new adaptive optics (AO) observations of
Class I protostars with our previously published AO data to investigate whether
Class I protostars with a widely separated companion (r>200 AU) are more likely
to also have a close companion (r<200 AU). In total, we observed 47 embedded
young stellar objects (YSOs) with either the Subaru natural guide star AO
system or the Keck laser guide star AO system. We found that targets with a
widely separated companion within 5,000 AU are not more likely to have a close
companion. However, targets with another YSO within a projected separation of
25,000 AU are much more likely to have a close companion. Most importantly,
every target with a close companion has another YSO within a projected
separation of 25,000 AU. We came to the same conclusions after considering a
restricted sample of targets within 500 pc and close companions wider than 50
AU to minimize incompleteness effects. The Orion star forming region was found
to have an excess of both close binaries and YSOs within 25,000 AU compared to
other star forming regions. We interpret these observations as strong evidence
that many close Class I binary stars form via ejections and that many of the
ejected stars become unbound during the Class I phase.Comment: 22 pages, 3 figures, 2 table
The Evolution of the Multiplicity of Embedded Protostars II: Binary Separation Distribution & Analysis
We present the Class I protostellar binary separation distribution based on
the data tabulated in the companion paper. We verify the excess of Class I
binary stars over solar-type main-sequence stars, especially at separations
beyond 500 AU. Although our sources are in nearby star forming regions
distributed across the entire sky (including Orion), none of our objects are in
a high stellar density environment. The binary separation distribution changes
significantly during the Class I phase, and the binary frequency at separations
greater than 1000 AU declines steadily with respect to spectral index. Despite
these changes, the binary frequency remains constant until the end of the Class
I phase, when it drops sharply. We propose a scenario to account for the
changes in the Class I binary separation distribution. This scenario postulates
that companions with a separation greater than ~1000 AU were ejected during the
Class 0 phase, but remain gravitationally bound due to the mass of the
envelope. As the envelope dissipates, these companions become unbound and the
binary frequency at wide separations declines. This scenario predicts that a
large number of Class 0 objects should be non-hierarchical multiple systems,
and that many Class I YSOs with a widely separated companion should also have a
very close companion. We also find that Class I protostars are not dynamically
pristine, and have experienced dynamical evolution before they are visible as
Class I objects. For the first time, evidence is presented showing that the
Class I binary frequency and the binary separation distribution strongly depend
on the star forming environment. The reason for this dependence remains
unclear.Comment: 33 pages, 16 figures, accepted by the Astronomical Journa
Binary energy source of the HH 250 outflow and its circumstellar environment
Herbig-Haro flows are signposts of recent major accretion and outflow
episodes. We aim to determine the nature and properties of the little-known
outflow source HH 250-IRS, which is embedded in the Aquila clouds. We have
obtained adaptive optics-assisted L-band images with the NACO instrument on the
Very Large Telescope (VLT), together with N- and Q-band imaging with VISIR also
on the VLT. Using the SINFONI instrument on the VLT we carried out H- and
K-band integral field spectroscopy of HH 250-IRS, complemented with spectra
obtained with the SpeX instrument at the InfraRed Telescope Facility (IRTF) in
the JHKL bands. Finally, the SubMillimeter Array (SMA) interferometer was used
to study the circumstellar environment of HH 250-IRS at 225 and 351 GHz with CO
(2-1) and CO (3-2) maps and 0.9 mm and 1.3 mm continuum images. The HH 250-IRS
source is resolved into a binary with 0''53 separation, corresponding to 120 AU
at the adopted distance of 225 pc. The individual components show heavily
veiled spectra with weak CO absorption indicative of late-type stars. Both are
Class I sources, but their spectral energy distributions between 1.5 m and
19 m differ markedly and suggest the existence of a large cavity around
one of the components. The millimeter interferometric observations indicate
that the gas mainly traces a circumbinary envelope or disk, while the dust
emission is dominated by one of the circumstellar envelopes. HH 250-IRS is a
new addition to the handful of multiple systems where the individual stellar
components, the circumstellar disks and a circumbinary disk can be studied in
detail, and a rare case among those systems in which a Herbig-Haro flow is
present.Comment: Accepted for publication by Astronomy and Astrophysic
A Photometrically and Morphologically Variable Infrared Nebula in L483
We present narrow and broad K-band observations of the Class 0/I source IRAS
18148-0440 that span 17 years. The infrared nebula associated with this
protostar in the L483 dark cloud is both morphologically and photometrically
variable on a time scale of only a few months. This nebula appears to be an
infrared analogue to other well-known optically visible variable nebulae
associated with young stars, such as Hubble's Variable Nebula. Along with
Cepheus A, this is one of the first large variable nebulae to be found that is
only visible in the infrared. The variability of this nebula is most likely due
to changing illumination of the cloud rather than any motion of the structure
in the nebula. Both morphological and photometric changes are observed on a
time scale only a few times longer than the light crossing time of the nebula,
suggesting very rapid intrinsic changes in the illumination of the nebula. Our
narrow-band observations also found that H_2 knots are found nearly twice as
far to the east of the source as to its west, and that H_2 emission extends
farther east of the source than the previously known CO outflow.Comment: 19 pages, 6 figures, 1 tabl
A Near-Infrared Spectroscopic Survey of Class I Protostars
We present the results of a near-IR spectroscopic survey of 110 Class I
protostars observed from 0.80 microns to 2.43 microns at a spectroscopic
resolution of R=1200. We find that Class I objects exhibit a wide range of
lines and the continuum spectroscopic features. 85% of Class I protostars
exhibit features indicative of mass accretion, and we found that the veiling
excess, CO emission, and Br Gamma emission are closely related. We modeled the
spectra to estimate the veiling excess (r_k) and extinction to each target. We
also used near-IR colors and emission line ratios, when available, to also
estimate extinction. In the course of this survey, we observed the spectra of
10 FU Orionis-like objects, including 2 new ones, as well as 3 Herbig Ae type
stars among our Class I YSOs. We used photospheric absorption lines, when
available, to estimate the spectral type of each target. Although most targets
are late type stars, there are several A and F-type stars in our sample.
Notably, we found no A or F class stars in the Taurus-Auriga or Perseus star
forming regions. There are several cases where the observed CO and/or water
absorption bands are deeper than expected from the photospheric spectral type.
We find a correlation between the appearance of the reflection nebula, which
traces the distribution of material on very large scales, and the near-IR
spectrum, which probes smaller scales. The spectra of the components of
spatially resolved protostellar binaries tend to be very similar. In particular
both components tend to have similar veiling and H_2 emission, inconsistent
with random selection from the sample as a whole. There is a strong correlation
between [Fe II] and H_2 emission, supporting previous results showing that H_2
emission in the spectra of young stars is usually shock excited by stellar
winds.Comment: 89 pages, 13 figures, 7 Table
The Brightening of Re50N: Accretion Event or Dust Clearing?
The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is
associated with a pair of reflection nebulae, Re50 and Re50N, which appeared
sometime between 1955 and 1979. We have found that a dramatic brightening of
Re50N has taken place sometime between 2006 and 2014. This could result if the
embedded source is undergoing a FUor eruption. However, the near-infrared
spectrum shows a featureless very red continuum, in contrast to the strong CO
bandhead absorption displayed by FUors. Such heavy veiling, and the high
luminosity of the protostar, is indicative of strong accretion but seemingly
not in the manner of typical FUors. We favor the alternative explanation that
the major brightening of Re50N and the simultaneous fading of Re50 is caused by
curtains of obscuring material that cast patterns of illumination and shadows
across the surface of the molecular cloud. This is likely occurring as an
outflow cavity surrounding the embedded protostar breaks through to the surface
of the molecular cloud. Several Herbig-Haro objects are found in the region.Comment: 8 pages, accepted by Ap
Second generation Robo-AO instruments and systems
The prototype Robo-AO system at the Palomar Observatory 1.5-m telescope is
the world's first fully automated laser adaptive optics instrument. Scientific
operations commenced in June 2012 and more than 12,000 observations have since
been performed at the ~0.12" visible-light diffraction limit. Two new infrared
cameras providing high-speed tip-tilt sensing and a 2' field-of-view will be
integrated in 2014. In addition to a Robo-AO clone for the 2-m IGO and the
natural guide star variant KAPAO at the 1-m Table Mountain telescope, a second
generation of facility-class Robo-AO systems are in development for the 2.2-m
University of Hawai'i and 3-m IRTF telescopes which will provide higher Strehl
ratios, sharper imaging, ~0.07", and correction to {\lambda} = 400 nm.Comment: 11 pages, 4 figures, 3 table
Modeling the Multiwavelength Evolution of the V960 Mon System
We study the evolution of the FU Ori object V960 Mon since its outburst,
using available multi-wavelength photometric time series over 8 years,
complemented by several epochs of moderate-dispersion spectrophotometry. We
find that the source fading can be well-described by a decrease in the
temperature of the inner disk, which results from a combination of decreasing
accretion rate and increasing inner disk radius. We model the system with a
disk atmosphere model that produces the observed variations in multi-band
photometry (this paper) and high resolution spectral lines (a companion paper).Comment: 15 pages, 13 figures, 2 tables, Accepted to Ap