We present the first mid-IR detection of the linear polarization toward the star CygOB2-12, a luminous blue hypergiant that, with Av of ~10 mag of foreground extinction, is a benchmark in the study ...of the properties of dust in the diffuse interstellar medium. The 8-13 micrometer spectropolarimetry, obtained with the CanariCam multi-mode camera at the Gran Telescopio Canarias (GTC), shows clear trends with wavelength characteristic of silicate grains aligned in the interstellar magnetic field. The maximum polarization, detected with 7.8 statistical significance near 10.2 micrometers, is (1.24 +/- 0.28) % with position angle (126 +/- 8) deg. We comment on these measurements in the context of recent models for the dust composition in the diffuse interstellar medium.
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.
We have made array camera images of the central parsec with 1 arcsec resolution at eight midinfrared wavelengths between 4.8 and 20.0 μm. The images are used to model the temperature, opacity and ...bolometric luminosity distributions of the emitting dust in the central parsec, as well as the dust extinction in the line of sight. Several new results emerge from the model calculations: 1) The compact IRS sources are all local peaks in the emitting dust temperature distribution. 2) The IRS source positions are local minima in the emitting dust opacity distribution. 3) The opacity and temperature distributions are generally complementary. 4) The compact IRS sources are very luminous, particularly the IRS3 and IRS1 (L ∼ 3 × 105 L⊙), and they make a significant contribution to the energy budget of infrared complex.
We used FIR and submillimeter continuum data from Herschel and the Atacama Pathfinder EXperiment (APEX) to fit pixel-by-pixel modified Planck SEDs to prestellar and protostellar clumps in the Census ...of High- and Medium-mass Protostars (CHaMP) (\(280^{\circ}<\ell<300^{\circ}\), \(-4^{\circ}<b<+2^{\circ}\)). We present maps of dust temperature (\(T_{\text{d}}\)) and H\(_2\) column density (\ncol) for molecular clumps in the Carina Nebula complex (Regions 9 through 11), and surrounding RCW 64 (Region 26). We compare the column densities of CO and H\(_2\) to chart regional variations in their correspondence, and derive maps of the CO abundance. We find the CO abundance varies by an order of magnitude or more across each region, averaging a few\(\times\)10\(^{-5}\) CO per H\(_2\), and that the CO abundance distribution across each clump is correlated in both form and magnitude with environmental conditions, especially \(T_{\text{d}}\). This demonstrates that no single CO abundance suffices to convert from \(N_{\text{CO}}\) to \ncol, even within a single molecular cloud. We also find that \(L/M\) traces \(T_{\text{d}}\) almost exclusively, and therefore is not an independent star formation tracer, but minima in \(T_{\text{d}}\) almost universally coincide with maxima in \ncol, implying that cooling and density enhancement must be simultaneous steps in prestellar clump evolution. Finally, based on generalized histogram N-PDFs of clump-scale (1-5 pc) and cloud-scale (\(\gtrsim10\) pc) samples, we could only obtain dual log-normal and power-law fits to \(\sim10\%\) of the clumps. The physical parameters derived from these fits approach theoretical expectations, but have largely unknown uncertainties, so we advise treating the results of N-PDF fitting with caution.
The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright FGKM dwarfs (within 50 pc) during 2016\(-\)2020 for low-mass planet detection and characterization using the TOU very high ...resolution optical spectrograph (R\(\approx\)100,000, 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 (\(V=4.4\) mag) on the sky with a super-Earth candidate. The planet candidate has a mass of 8.47\(\pm0.47M_{\rm Earth}\), period of \(42.38\pm0.01\) d, and eccentricity of \(0.04^{+0.05}_{-0.03}\). 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 (39\(-\)44.5 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.
A Monte Carlo model of radiative transfer in multi-phase dusty media is
applied to the situation of stars and clumpy dust in a sphere or a disk. The
distribution of escaping and absorbed photons are ...shown for various filling
factors and densities. Analytical methods of approximating the escaping
fraction of radiation, based on the Mega-Grains approach, are discussed.
Comparison with the Monte Carlo results shows that the escape probability
formulae provide a reasonable approximation of the escaping/absorbed fractions,
for a wide range of parameters characterizing a clumpy dusty medium. A possibly
more realistic model of the interstellar medium is one in which clouds have a
self-similar hierarchical structure of denser and denser clumps within clumps,
resulting in a fractal distribution of gas and dust. Monte Carlo simulations of
radiative transfer in such multi-phase fractal media are compared with the
two-phase clumpy case.
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.
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.
A new infrared array camera system using a Hughes/SBRC 58x62 pixel hybrid Si: Ga array detector has been successfully applied to high-background 5-18 µm astronomical imaging observations. The ...off-axis reflective optical system minimizes thermal background loading and produces diffraction-limited images with negligible spatial distortion. The noise equivalent flux density (NEFD) of the camera at 10 µm on the 3.0-m NASA/Infrared Telescope Facility with broadband (Δλ/λ= 0.1) interference filters and 0.26 arcsec pixel is NEFD= 0.01 Jy min~ 1/2 pixel" 1 (1σ), and it operates at a frame rate of 30 Hz with no compromise in observational efficiency. The electronic and optical design of the camera, its photometric characteristics, examples of observational results, and techniques for successful array imaging in a high-background astronomical application are discussed.
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