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We present spatially resolved ($0.1 - 1.0$) radio maps of Neptune taken from the Very Large Array and Atacama Large Submillimeter/Millimeter Array between $2015-2017$. Combined, these observations probe from just below the main methane cloud deck at $sim 1$ bar down to the NH$_4$SH cloud at $sim50$ bar. Prominent latitudinal variations in the brightness temperature are seen across the disk. Depending on wavelength, the south polar region is $5-40$ K brighter than the mid-latitudes and northern equatorial region. We use radiative transfer modeling coupled to Markov Chain Monte Carlo methods to retrieve H$_2$S, NH$_3$, and CH$_4$ abundance profiles across the disk, though only strong constraints can be made for H$_2$S. Below all cloud formation, the data are well fit by $53.8^{+18.9}_{-13.4}times$ and $3.9^{+2.1}_{-3.1}times$ protosolar enrichment in the H$_2$S and NH$_3$ abundances, respectively, assuming a dry adiabat. Models in which the radio-cold mid-latitudes and northern equatorial region are supersaturated in H$_2$S are statistically favored over models following strict thermochemical equilibrium. H$_2$S is more abundant at the equatorial region than at the poles, indicative of strong, persistent global circulation. Our results imply that Neptunes sulfur-to-nitrogen ratio exceeds unity as H$_2$S is more abundant than NH$_3$ in every retrieval. The absence of NH$_3$ above 50 bar can be explained either by partial dissolution of NH$_3$ in an ionic ocean at GPa pressures or by a planet formation scenario in which hydrated clathrates preferentially delivered sulfur rather than nitrogen onto planetesimals, or a combination of these hypotheses.
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Submillimeter emission lines of carbon monoxide (CO) in Titans atmosphere provide excellent probes of atmospheric temperature due to the molecules long chemical lifetime and stable, well constrained volume mixing ratio. Here we present the analysis of 4 datasets obtained with the Atacama Large Millimeter/Submillimeter Array (ALMA) from 2012 to 2015 that contain strong CO rotational transitions. Utilizing ALMAs high spatial resolution in the 2012, 2014, and 2015 observations, we extract spectra from 3 separate regions on Titans disk using datasets with beam sizes of ~0.3. Temperature profiles retrieved by the NEMESIS radiative transfer code are compared to Cassini Composite Infrared Spectrometer (CIRS) and radio occultation science results from similar latitude regions. Small seasonal variations in atmospheric temperature are present from 2012 to 2015 in the stratosphere and mesosphere (~100-500 km) of spatially resolved regions. We measure the stratopause (320 km) to increase in temperature by 5 K in northern latitudes from 2012-2015, while temperatures rise throughout the stratosphere at lower latitudes. While retrieved temperature profiles cover a range of latitudes in these observations, deviations from CIRS nadir maps and radio occultation measurements convolved with the ALMA beam-footprint are not found to be statistically significant, and discrepancies are often found to be less than 5 K throughout the atmosphere. ALMAs excellent sensitivity in the lower stratosphere (60-300 km) provides a highly complementary dataset to contemporary CIRS and radio science observations. The demonstrated utility of CO emission lines in the submillimeter as a tracer of Titans atmospheric temperature lays the groundwork for future studies of other molecular species, as temperature profiles are found to consistently vary with latitude in all three years by up to 15 K.
We present ALMA and VLA spatial maps of the Uranian atmosphere taken between 2015 and 2018 at wavelengths from 1.3 mm to 10 cm, probing pressures from $sim$1 to $sim$50 bar at spatial resolutions from 0.1 to 0.8. Radiative transfer modeling was performed to determine the physical origin of the brightness variations across Uranuss disk. The radio-dark equator and midlatitudes of the planet (south of $sim$50$^circ$ N) are well fit by a deep H$_2$S mixing ratio of $8.7_{-1.5}^{+3.1}times10^{-4}$ ($37_{-6}^{+13}times$ Solar) and a deep NH$_3$ mixing ratio of $1.7_{-0.4}^{+0.7}times10^{-4}$ ($1.4_{-0.3}^{+0.5}times$ Solar), in good agreement with literature models of Uranuss disk-averaged spectrum. The north polar region is very bright at all frequencies northward of $sim$50$^circ$N, which we attribute to strong depletions extending down to the NH$_4$SH layer in both NH$_3$ and H$_2$S relative to the equatorial region; the model is consistent with an NH$_3$ abundance of $4.7_{-1.8}^{+2.1} times 10^{-7}$ and an H$_2$S abundance of $<$$1.9times10^{-7}$ between $sim$20 and $sim$50 bar. Combining this observed depletion in condensible molecules with methane-sensitive near-infrared observations from the literature suggests large-scale downwelling in the north polar vortex region from $sim$0.1 to $sim$50 bar. The highest-resolution maps reveal zonal radio-dark and radio-bright bands at 20$^circ$S, 0$^circ$, and 20$^circ$N, as well as zonal banding within the north polar region. The difference in brightness is a factor of $sim$10 less pronounced in these bands than the difference between the north pole and equator, and additional observations are required to determine the temperature, composition and vertical extent of these features.
It has been demonstrated that the time variability of a stars brightness at different frequencies can be used to infer its surface gravity, radius, mass, and age. With large samples of light curves now available from Kepler and K2, and upcoming surveys like TESS, we wish to quantify the overall information content of this data and identify where the information resides. As a first look into this question we ask which stellar parameters we can predict from the brightness variations in red-giant stars data and to what precision, using a data-driven model. We demonstrate that the long-cadence (30-minute) Kepler light curves for 2000 red-giant stars can be used to predict their $T_{rm eff}$ and $log g$. Our inference makes use of a data-driven model of a part of the autocorrelation function (ACF) of the light curve, where we posit a polynomial relationship between stellar parameters and the ACF pixel values. We find that this model, trained using 1000 stars, can be used to recover the temperature $T_{rm eff}$ to $<$100 K, the surface gravity to $<$ 0.1 dex, and the asteroseismic power-spectrum parameters $rm u_{max}$ and $rm Delta{ u}$ to $<11$ $mu$Hz and $<0.9$ $mu$Hz ($lesssim$ 15%). We recover $T_{rm eff}$ from range of time-lags 0.045 $<$ $T_{rm lag}$ $<$ 370 days and the $log g$, $rm u_{max}$ and $rm Delta{ u}$ from the range 0.045 $<$ $T_{rm lag}$ $<$ 35 days. We do not discover any information about stellar metallicity. The information content of the data about each parameter is empirically quantified using this method, enabling comparisons to theoretical expectations about convective granulation.
Extreme outbursts in young stars may be a common stage of pre-main-sequence stellar evolution. These outbursts, caused by enhanced accretion and accompanied by increased luminosity, can also strongly impact the evolution of the circumstellar environment. We present ALMA and VLA observations of EX Lupi, a prototypical outburst system, at 100 GHz, 45 GHz, and 15 GHz. We use these data, along with archival ALMA 232 GHz data, to fit radiative transfer models to EX Lupis circumstellar disk in its quiescent state following the extreme outburst in 2008. The best fit models show a compact disk with a characteristic dust radius of 45 au and a total mass of 0.01 M$_{odot}$. Our modeling suggests grain growth to sizes of at least 3 mm in the disk, possibly spurred by the recent outburst, and an ice line that has migrated inward to $0.2-0.3$ au post-outburst. At 15 GHz, we detected significant emission over the expected thermal disk emission which we attribute primarily to stellar (gyro)synchrotron and free-free disk emission. Altogether, these results highlight what may be a common impact of outbursts on the circumstellar dust.
Most extrasolar planets have been detected by their influence on their parent star, typically either gravitationally (the Doppler method) or by the small dip in brightness as the planet blocks a portion of the star (the transit method). Therefore, the accuracy with which we know the masses and radii of extrasolar planets depends directly on how well we know those of the stars, the latter usually determined from the measured stellar surface gravity, logg. Recent work has demonstrated that the short-timescale brightness variations (flicker) of stars can be used to measure logg to a high accuracy of ~0.1-0.2 dex (Bastien et al. 2013). Here, we use flicker measurements of 289 bright (Kepmag<13) candidate planet-hosting stars with Teff=4500-6650 K to re-assess the stellar parameters and determine the resulting impact on derived planet properties. This re-assessment reveals that for the brightest planet-host stars, an astrophysical bias exists that contaminates the stellar sample with evolved stars: nearly 50% of the bright planet-host stars are subgiants. As a result, the stellar radii, and hence the radii of the planets orbiting these stars, are on average 20-30% larger than previous measurements had suggested.
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