13 research outputs found
Analytical Approximations for Calculating the Escape and Absorption of Radiation in Clumpy Dusty Environments
We present analytical approximations for calculating the scattering,
absorption and escape of nonionizing photons from a spherically symmetric
two-phase clumpy medium, with either a central point source of isotropic
radiation, a uniform distribution of isotropic emitters, or uniformly
illuminated by external sources. The analytical approximations are based on the
mega-grains model of two-phase clumpy media, as proposed by Hobson & Padman,
combined with escape and absorption probability formulae for homogeneous media.
The accuracy of the approximations is examined by comparison with 3D Monte
Carlo simulations of radiative transfer, including multiple scattering. Our
studies show that the combined mega-grains and escape/absorption probability
formulae provide a good approximation of the escaping and absorbed radiation
fractions for a wide range of parameters characterizing the medium. A realistic
test is performed by modeling the absorption of a starlike source of radiation
by interstellar dust in a clumpy medium, and by calculating the resulting
equilibrium dust temperatures and infrared emission spectrum of both the clumps
and the interclump medium. In particular, we find that the temperature of dust
in clumps is lower than in the interclump medium if clumps are optically thick.
Comparison with Monte Carlo simulations of radiative transfer in the same
environment shows that the analytic model yields a good approximation of dust
temperatures and the emerging UV to FIR spectrum of radiation for all three
types of source distributions mentioned above. Our analytical model provides a
numerically expedient way to estimate radiative transfer in a variety of
interstellar conditions and can be applied to a wide range of astrophysical
environments, from star forming regions to starburst galaxies.Comment: 55 pages, 27 figures. ApJ 523 (1999), in press. Corrected equations
and text so as to be same as ApJ versio
GTC/CanariCam Mid-IR Polarimetry of Magnetic Fields in Star-Forming Region W51 IRS2
We present 0.4 arcsec-resolution imaging polarimetry at 8.7, 10.3, and 12.5
microns, obtained with CanariCam at the Gran Telescopio Canarias, of the
central region of W51 IRS2. The polarization, as high as 14 percent, arises
from silicate particles aligned by the interstellar magnetic field. We
separate, or unfold, the polarization of each sightline into emission and
absorption components, from which we infer the morphologies of the
corresponding projected magnetic fields that thread the emitting and
foreground-absorbing regions. We conclude that the projected magnetic field in
the foreground material is part of the larger-scale ambient field. The
morphology of the projected magnetic field in the mid-IR emitting region
spanning the cometary HII region W51 IRS2W is similar to that in the absorbing
region. Elsewhere, the two magnetic fields differ significantly with no clear
relationship between them. The magnetic field across the W51 IRS2W cometary
core appears to be an integral part of a champagne outflow of gas originating
in the core and dominating the energetics there. The bipolar outflow, W51north
jet, that appears to originate at or near SMA1/N1 coincides almost exactly with
a clearly demarcated north-south swath of lower polarization. While
speculative, comparison of mid-IR and submm polarimetry on two different scales
may support a picture in which SMA1/N1 plays a major role in the magnetic field
structure across W51 IRS2.Comment: To be published in the Astrophysical Journa
The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey
The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright
FGKM dwarfs (within 50 pc) during 20162020 for low-mass planet detection and
characterization using the TOU very high resolution optical spectrograph
(R100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic
Spectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot
survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon
in 2016 to launch the survey. Here we report the first planet detection from
DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is
the second brightest star ( mag) on the sky with a super-Earth
candidate. The planet candidate has a mass of 8.47,
period of d, and eccentricity of . This RV
signal was independently detected by Diaz et al. (2018), but they could not
confirm if the signal is from a planet or from stellar activity. The orbital
period of the planet is close to the rotation period of the star (3944.5 d)
measured from stellar activity indicators. Our high precision photometric
campaign and line bisector analysis of this star do not find any significant
variations at the orbital period. Stellar RV jitters modeled from star spots
and convection inhibition are also not strong enough to explain the RV signal
detected. After further comparing RV data from the star's active magnetic phase
and quiet magnetic phase, we conclude that the RV signal is due to
planetary-reflex motion and not stellar activity.Comment: 13 pages, 17 figures, Accepted for publication in MNRA
The first super-Earth detection from the high cadence and high radial velocity precision Dharma Planet Survey
The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright FGKM dwarfs (within 50 pc) during 2016â2020 for low-mass planet detection and characterization using the TOU very high resolution optical spectrograph (â Râ100000â , 380â900ânm). TOU was initially mounted to the 2-m Automatic Spectroscopic Telescope at Fairborn Observatory in 2013â2015 to conduct a pilot survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon in 2016 to launch the survey. Here, we report the first planet detection from DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is the second brightest star (V = 4.4 mag) on the sky with a super-Earth candidate. The planet candidate has a mass of 8.47 ± 0.47MEarth, period of 42.38 ± 0.01 d, and eccentricity of 0.04+0.05â0.03â . This radial velocity (RV) signal was independently detected by DĂaz et al., but they could not confirm if the signal is from a planet or stellar activity. The orbital period of the planet is close to the rotation period of the star (39â44.5 d) measured from stellar activity indicators. Our high precision photometric campaign and line bisector analysis of this star do not find any significant variations at the orbital period. Stellar RV jitters modelled from star-spots and convection inhibition are also not strong enough to explain the RV signal detected. After further comparing RV data from the starâs active magnetic phase and quiet magnetic phase, we conclude that the RV signal is due to planetary-reflex motion and not stellar activity
CIRCE: The Canarias InfraRed Camera Experiment for the Gran Telescopio Canarias
The Canarias InfraRed Camera Experiment (CIRCE) is a near-infrared (1-2.5Όm) imager, polarimeter and low-resolution spectrograph operating as a visitor instrument for the Gran Telescopio Canarias (GTC) 10.4-m telescope. It was designed and built largely by graduate students and postdocs, with help from the University of Florida (UF) astronomy engineering group, and is funded by the UF and the US National Science Foundation. CIRCE is intended to help fill the gap in near-infrared capabilities prior to the arrival of Especrografo Multiobjecto Infra-Rojo (EMIR) to the GTC and will also provide the following scientific capabilities to compliment EMIR after its arrival: high-resolution imaging, narrowband imaging, high-time-resolution photometry, imaging polarimetry, and low resolution spectroscopy. In this paper, we review the design, fabrication, integration, lab testing, and on-sky performance results for CIRCE. These include a novel approach to the opto-mechanical design, fabrication, and alignment. © 2018 World Scientific Publishing Company.CIRCE was developed with support of the University of Florida and the National Science Foundation (NSF grant AST-0352664). The CIRCE team gratefully acknowledges the collaborative support of the Gran Telescopio Canarias management and staff in this endeavor - both the current staff and, in particular, the long-standing support of the previous Director Pedro Alvarez and the previous Project Scientist J. M. Rodriguez