67 research outputs found
Westbrook's Molecular Gun: Discovery of Near-IR Micro-Structures in AFGL 618
We present high-sensitivity near-IR images of a carbon-rich proto-planetary
nebula, AFGL 618, obtained with the Subaru Telescope. These images have
revealed ``bullets'' and ``horns'' extending farther out from the edges of the
previously known bipolar lobes. The spatial coincidence between these near-IR
micro-structures and the optical collimated outflow structure, together with
the detection of shock-excited, forbidden IR lines of atomic species, strongly
suggests that these bullets and horns represent the locations from which
[\ion{Fe}{2}] IR lines arise. We have also discovered CO clumps moving at km s at the positions of the near-IR bullets by re-analyzing the
existing CO interferometry data. These findings indicate that
the near-IR micro-structures represent the positions of shocked surfaces at
which fast-moving molecular clumps interface with the ambient circumstellar
shell.Comment: 2 figures. To appear in the ApJ Letter
Multiple Molecular H2 Outflows in AFGL 618
We report high spatial (0.5 arcsec) and high spectral (9 km/s) resolution
spectro-imaging of the 2.12 micron H2 1-0 S(1) line in the proto-planetary
nebula AFGL 618 using BEAR at the CFHT. The observations reveal the presence of
multiple, high-velocity, molecular outflows that align with the remarkable
optical jets seen in HST images. The structure and kinematics of the outflows
show how jets interact with circumstellar gas and shape the environment in
which planetary nebulae form.Comment: 14 pages, 5 figures. To appear in The Astrophysical Journal Letter
Physical structure of the protoplanetary nebula CRL618. I. Optical long-slit spectroscopy and imaging
In this paper (paper I) we present optical long-slit spectroscopy and imaging
of the protoplanetary nebula CRL618. The optical lobes of CRL618 consist of
shock-excited gas, which emits many recombination and forbidden lines, and
dust, which scatters light from the innermost regions. From the analysis of the
scattered Halpha emission, we derive a nebular inclination of i=24+-6 deg. The
spectrum of the innermost part of the east lobe (visible as a bright, compact
nebulosity close to the star in the Halpha HST image) is remarkably different
from that of the shocked lobes but similar to that of the inner HII region,
suggesting that this region represents the outermost parts of the latter. We
find a non-linear radial variation of the gas velocity along the lobes.
The largest projected LSR velocities (~80 km/s) are measured at the tips of
the lobes, where the direct images show the presence of compact bow-shaped
structures. The velocity of the shocks in CRL618 is in the range ~75-200 km/s,
as derived from diagnostic line ratios and line profiles. We report a
brightening (weakening) of [OIII]5007AA ([OI]6300AA) over the last ~10 years
that may indicate a recent increase in the speed of the exciting shocks. From
the analysis of the spatial variation of the nebular extinction, we find a
large density contrast between the material inside the lobes and beyond them:
the optical lobes seem to be `cavities' excavated in the AGB envelope by
interaction with a more tenuous post-AGB wind. The electron density, with a
mean value n_e~5E3-1E4 cm-3, shows significant fluctuations but no systematic
decrease along the lobes, in agreement with most line emission arising in a
thin shell of shocked material (the lobe walls) rather than in the post-AGB
wind filling the interior of the lobes. (...)Comment: 21 pages, 10 figures, accepted for publication in Ap
Investigating the Near-Infrared Properties of Planetary Nebula II. Medium Resolution Spectra
We present medium-resolution (R~700) near-infrared (lambda = 1 - 2.5 micron)
spectra of a sample of planetary nebulae (PNe). A narrow slit was used which
sampled discrete locations within the nebulae; observations were obtained at
one or more positions in the 41 objects included in the survey. The PN spectra
fall into one of four general categories: H I emission line-dominated PNe, H I
and H_2 emission line PNe, H_2-dominated PNe, and continuum-dominated PNe.
These categories correlate with morphological type, with the elliptical PNe
falling into the first group, and the bipolar PNe primarily in the H_2 and
continuum emission groups. Other spectral features were observed in all
categories, such as continuum emission from the central star, C_2, CN, and CO
emission, and warm dust continuum emission.
Molecular hydrogen was detected for the first time in four PNe. An excitation
analysis was performed using the H_2 line ratios for all of the PN spectra in
the survey where a sufficient number of lines were observed. One unexpected
result from this analysis is that the H_2 is excited by absorption of
ultraviolet photons in most of the PNe surveyed, although for several PNe in
our survey collisional excitation in moderate velocity shocks plays an
important role. The correlation between bipolar morphology and H_2 emission has
been strengthened with the new detections of H_2 in this survey.Comment: 13 pages, 8 tables, 33 figure
Panchromatic Observations of the Textbook GRB 110205A: Constraining Physical Mechanisms of Prompt Emission and Afterglow
We present a comprehensive analysis of a bright, long duration (T(sub 90) approx. 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb and BOOTES telescopes when the GRB was still radiating in the gamma-ray band. Thanks to its long duration, nearly 200 s of observations were obtained simultaneously from optical, X-ray to gamma-ray (1 eV - 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution across 6 orders of magnitude in energy during the prompt emission phase. In particular, by fitting the time resolved prompt spectra, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard GRB synchrotron emission model in the fast cooling regime. Although the prompt optical emission is brighter than the extrapolation of the best fit X/ -ray spectra, it traces the -ray light curve shape, suggesting a relation to the prompt high energy emission. The synchrotron + synchrotron self-Compton (SSC) scenario is disfavored by the data, but the models invoking a pair of internal shocks or having two emission regions can interpret the data well. Shortly after prompt emission (approx. 1100 s), a bright (R = 14.0) optical emission hump with very steep rise ( alpha approx. 5.5) was observed which we interpret as the emission from the reverse shock. It is the first time that the rising phase of a reverse shock component has been closely observed
Panchromatic observations of the textbook GRB 110205A: Constraining physical mechanisms of prompt emission and afterglow
We present a comprehensive analysis of a bright, long-duration (T 90 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the γ-ray band, with optical light curve showing correlation with γ-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to γ-ray (1 eV to 5MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (1100s), a bright (R = 14.0) optical emission hump with very steep rise (α 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (R GRB 3 × 1013cm), initial Lorentz factor of the outflow (Γ0 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget. © 2012. The American Astronomical Society. All rights reserved.
Does Vesta Have Moons?: Dawn's Search for Satellites
Upon approach to asteroid 4 Vesta, the Dawn mission included a dedicated satellite search observation of the operational sphere of the spacecraft around Vesta. Discovery of moons of Vesta would constrain theories of satellite f()rmation. The sequence using the framing camera and clear filter includes three mosaics of six stations acquired on July 9-10. 2011. Each station consists of four sets with three different exposures, 1.5,20 and 270 s. We also processed and scanned the optical navigation sequences until Vesta filled the field of view. Analysis of images involves looking for moving objects in the mosaics and identifying catalogued stars, subtracting them from the image and examining residual objects for evidence of bodies in orbit around Vesta. Celestial coordinates were determined using Astrometry.net, an astrometry calibration service (http://astrometry.net/use.html). We processed the images by subtracting dark and bias fields and dividing by a Hatfield. Images were further filtered subtracting a box car filter (9x9 average) to remove effects of scattered light from Vesta itself. Images were scanned by eye for evidence of motion in directions different from the background stars. All objects were compared with Hubble Space Telescope's Guide Star Catalogue and US Naval Observatory's UCAC3 catalog. We report findings from these observations and analysis, including limits of magnitude, size and motion of objects in orbit around Vesta. We gratefully acknowledge modifications made to Astrometrica http://www.astrometrica.at/ for purposes of this effort
Martian atmosphere as observed by VIRTIS‐M on Rosetta spacecraft
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95134/1/jgre2651.pd
Panchromatic Observations of the Textbook GRB 110205A: Constraining Physical Mechanisms of Prompt Emission and Afterglow
We present a comprehensive analysis of a bright, long-duration ( T 90 ~ 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift /UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the γ-ray band, with optical light curve showing correlation with γ-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to γ-ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (~1100 s), a bright ( R = 14.0) optical emission hump with very steep rise (α ~ 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission ( R GRB ~ 3 × 10 13 cm), initial Lorentz factor of the outflow (Γ 0 ~ 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98559/1/0004-637X_751_2_90.pd
Vesta High SNR Differential Photometry
Our goal is to obtain ground-base high SNR color
variation of Vesta in the 7 color bands of the NASA
Dawn spacecraft missio
- …