97 research outputs found
The curious morphology and orientation of Orion proplyd HST-10
HST-10 is one of the largest proplyds in the Orion Nebula and is located
approximately 1' SE of the Trapezium. Unlike other proplyds in Orion, however,
the long-axis of HST-10 does not align with theta 1 C Ori, but is instead
aligned with the rotational axis of the HST-10 disk. This cannot be easily
explained using current photo-evaporation models. In this letter, we present
high spatial resolution near-infrared images of the Orion proplyd HST-10 using
Keck/NIRC2 with the Laser Guide Star Adaptive Optics system, along with
multi-epoch analysis of HH objects near HST-10 using Hubble Space Telescope
WFPC2 and ACS cameras. Our narrow-band near-IR images resolve the proplyd
ionization front (IF) and circumstellar disk down to 23 AU at the distance to
Orion in Br gamma, He I, H_2, and PAH emission. Br gamma and He I emission
primarily trace the IF (with the disk showing prominently in silhouette), while
the H_2 and PAH emission trace the surface of the disk itself. PAH emission
also traces small dust grains within the proplyd envelope which is asymmetric
and does not coincide with the IF. The curious morphology of the PAH emission
may be due to UV-heating by both theta 1C Ori and theta 2A Ori. Multi-epoch HST
images of the HST-10 field show proper motion of 3 knots associated with HH
517, clearly indicating that HST-10 has a jet. We postulate that the
orientation of HST-10 is determined by the combined ram-pressure of this jet
and the FUV-powered photo-ablation flow from the disk surface.Comment: 12 pages, 2 figures. Accepted for publication in ApJ Letters, 4 Nov
201
The Slitmask Alignment Tool: robust, efficient, and astronomer-friendly software for aligning multi-object slitmasks
Multi-object spectroscopy via custom slitmasks is a key capability on three instruments at the W. M. Keck Observatory. Before observers can acquire spectra they must complete a complex procedure to align each slit with its corresponding science target. We developed the Slitmask Alignment Tool (SAT), to replace a complex, inefficient, and error-prone slitmask alignment process that often resulted in lost sky time for novice and experienced observers alike. The SAT accomplishes rapid initial mask alignment, prevents field misidentification, accurately predicts alignment box image locations, corrects for flexure-induced image displacement, verifies the instrument and exposure configuration, and accommodates both rectangular and trapezoidal alignment box shapes. The SAT is designed to lead observers through the alignment process and coordinate image acquisition with instrument and telescope moves to improve efficiencies. By simplifying the process to just a few mouse clicks, the SAT enables even novice observers to achieve robust, efficient, and accurate alignment of slitmasks on all three Keck instruments supporting multislit spectroscopy, saving substantial observing time
Thermal Dust Emission from Proplyds, Unresolved Disks, and Shocks in the Orion Nebula
We present a new 11.7 micron mosaic image of the Orion nebula obtained with
T-ReCS on Gemini South. The map includes the BN/KL region, the Trapezium, and
OMC-1 South. Excluding BN/KL, we detect 91 point sources, with 27 known
proplyds and over 30 ``naked'' stars showing no extended structure in HST
images. Within the region we surveyed, 80 percent of known proplyds show
detectable emission, almost 40 percent of naked stars are detected at 11.7
micron, and the fraction of all visible sources with IR excess emission is
roughly 50 percent. Thermal dust emission from stars with no extended structure
in HST images means that they have dust disks comparable to the size of our
solar system. Proplyds and stars with IR excess show a clear anti-correlation
in their spatial distribution, with proplyds clustered close to theta1C, and
other infrared sources found farther away. We suspect that the clustered
proplyds trace the youngest 0.5 Myr age group associated with the Trapezium,
while the more uniformly-distributed sources trace the older 1-2 Myr population
of the ONC. This suggests that small disks persist for a few Myr in irradiated
environments, and hints that hierarchical sub-clustering has been important.
Within 30 arcsec of theta1C, all proplyds are detected at 11.7 micron. The star
theta1D is associated with the most prominent mid-IR dust arc in the nebula. We
propose that this arc is the consequence of theta1D being the closest member of
the Trapezium to the background cloud. Finally, we detect dust emission from HH
jets in Orion, including HH202, HH529, HH513, and HH514. This is the first
detection of mid-IR continuum emission from dust in the body of a collimated HH
jet or bow shock.Comment: accepted by AJ. 27 pages, 11 figs, 4 color figs. If you actually want
to see the figures, download this version:
ftp://origins.colorado.edu/pub/nathans/smith.trecs.pd
Spectral classification of the brightest objects in the galactic star forming region W40
We present high S/N, moderate resolution near-infrared spectra, as well as 10
micron imaging, for the brightest members of the central stellar cluster in the
W40 HII region, obtained using the SpeX and MIRSI instruments at NASA's
Infrared Telescope Facility. Using these observations combined with archival
Spitzer Space Telescope data, we have determined the spectral classifications,
extinction, distances, and spectral energy distributions for the brightest
members of the cluster. Of the eight objects observed, we identify four main
sequence (MS) OB stars, two Herbig Ae/Be stars, and two low-mass young stellar
objects. Strong HeI absorption at 1.083 micron in the MS star spectra strongly
suggests that at least some of these sources are in fact close binaries. Two
out of the four MS stars also show significant infrared excesses typical of
circumstellar disks. Extinctions and distances were determined for each MS star
by fitting model stellar atmospheres to the SEDs. We estimate a distance to the
cluster of between 455 and 535 pc, which agrees well with earlier (but far less
precise) distance estimates. We conclude that the late-O star we identify is
the dominant source of LyC luminosity needed to power the W40 HII region and is
the likely source of the stellar wind that has blown a large (~4 pc)
pinched-waist bubble observed in wide field mid-IR images. We also suggest that
3.6 cm radio emission observed from some of the sources in the cluster is
likely not due to emission from ultra-compact HII regions, as suggested in
other work, due to size constraints based on our derived distance to the
cluster. Finally, we also present a discussion of the curious source IRS 3A,
which has a very strong mid-IR excess (despite its B3 MS classification) and
appears to be embedded in a dusty envelope roughly 2700 AU in size.Comment: Accepted for publication in The Astronomical Journal. 29 pages, 10
figure
The Slitmask Alignment Tool: robust, efficient, and astronomer-friendly software for aligning multi-object slitmasks
Multi-object spectroscopy via custom slitmasks is a key capability on three instruments at the W. M. Keck Observatory. Before observers can acquire spectra they must complete a complex procedure to align each slit with its corresponding science target. We developed the Slitmask Alignment Tool (SAT), to replace a complex, inefficient, and error-prone slitmask alignment process that often resulted in lost sky time for novice and experienced observers alike. The SAT accomplishes rapid initial mask alignment, prevents field misidentification, accurately predicts alignment box image locations, corrects for flexure-induced image displacement, verifies the instrument and exposure configuration, and accommodates both rectangular and trapezoidal alignment box shapes. The SAT is designed to lead observers through the alignment process and coordinate image acquisition with instrument and telescope moves to improve efficiencies. By simplifying the process to just a few mouse clicks, the SAT enables even novice observers to achieve robust, efficient, and accurate alignment of slitmasks on all three Keck instruments supporting multislit spectroscopy, saving substantial observing time
The MOSFIRE Deep Evolution Field (MOSDEF) Survey: Rest-Frame Optical Spectroscopy for ~1500 H-Selected Galaxies at 1.37 < z < 3.8
In this paper we present the MOSFIRE Deep Evolution Field (MOSDEF) survey.
The MOSDEF survey aims to obtain moderate-resolution (R=3000-3650) rest-frame
optical spectra (~3700-7000 Angstrom) for ~1500 galaxies at 1.37<z<3.80 in
three well-studied CANDELS fields: AEGIS, COSMOS, and GOODS-N. Targets are
selected in three redshift intervals: 1.37<z<1.70, 2.09<z<2.61, and
2.95<z<3.80, down to fixed H_AB (F160W) magnitudes of 24.0, 24.5 and 25.0,
respectively, using the photometric and spectroscopic catalogs from the 3D-HST
survey. We target both strong nebular emission lines (e.g., [OII], Hbeta,
[OIII], 5008, Halpha, [NII], and [SII]) and stellar continuum and absorption
features (e.g., Balmer lines, Ca-II H and K, Mgb, 4000 Angstrom break). Here we
present an overview of our survey, the observational strategy, the data
reduction and analysis, and the sample characteristics based on spectra
obtained during the first 24 nights. To date, we have completed 21 masks,
obtaining spectra for 591 galaxies. For ~80% of the targets we derive a robust
redshift from either emission or absorption lines. In addition, we confirm 55
additional galaxies, which were serendipitously detected. The MOSDEF galaxy
sample includes unobscured star-forming, dusty star-forming, and quiescent
galaxies and spans a wide range in stellar mass (~10^9-10^11.5 Msol) and star
formation rate (~10^0-10^3 Msol/yr). The spectroscopically confirmed sample is
roughly representative of an H-band limited galaxy sample at these redshifts.
With its large sample size, broad diversity in galaxy properties, and wealth of
available ancillary data, MOSDEF will transform our understanding of the
stellar, gaseous, metal, dust, and black hole content of galaxies during the
time when the universe was most active.Comment: Accepted for publication in ApJS; 28 pages, 19 figures; MOSDEF
spectroscopic redshifts available at
http://mosdef.astro.berkeley.edu/Downloads.htm
- …