Katherine de Kleer

A Nearby M Star with Three Transiting Super-Earths Discovered by K2

Small, cool planets represent the typical end-products of planetary formation. Studying the architectures of these systems, measuring planet masses and radii, and observing these planets’ atmospheres during transit directly informs theories of planet assembly, migration, and evolution. Here we report the discovery of three small planets orbiting a bright (Ks = 8:6 mag) M0 dwarf using data collected as part of K2, the new ecliptic survey using the re-purposed Kepler spacecraft. Stellar spectroscopy and K2 photometry indicate that the system hosts three transiting planets with radii 1.5 { 2.1 R , straddling the transition region between rocky and increasingly volatile-dominated compositions. With orbital periods of 10{45 days the planets receive just 1.5{10 the ux incident on Earth, making these some of the coolest small planets known orbiting a nearby star; planet d is located near the inner edge of the system’s habitable zone. The bright, low-mass star makes this system an excellent laboratory to determine the planets’ masses via Doppler spectroscopy and to constrain their atmospheric compositions via transit spectroscopy. This discovery demonstrates the power of K2 and future space-based transit searches to nd many fascinating objects of interest. Subject headings: EPIC 201367065| techniques: photometric | techniques: spectroscopic | eclipses

A PROGRADE, LOW-INCLINATION ORBIT FOR THE VERY HOT JUPITER WASP-3b*

We present new spectroscopic and photometric observations of the transiting exoplanetary system WASP-3. Spectra obtained during two separate transits exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the sky-projected angle between the planetary orbital axis and the stellar rotation axis, λ = 3.3^(+2.5)_(–4.4) deg. This alignment between the axes suggests that WASP-3b has a low orbital inclination relative to the equatorial plane of its parent star. During our first night of spectroscopic measurements, we observed an unexpected redshift briefly exceeding the expected sum of the orbital and RM velocities by 140 m s^(–1). This anomaly could represent the occultation of material erupting from the stellar photosphere, although it is more likely to be an artifact caused by moonlight scattered into the spectrograph.

Spatially resolved m-band emission from io's Loki Patera-fizeau imaging at the 22.8 m LBT

The Large Binocular Telescope Interferometer mid-infrared camera, LMIRcam, imaged Io on the night of 2013 December 24 UT and detected strong M-band (4.8 μm) thermal emission arising from Loki Patera. The 22.8 m baseline of the Large Binocular Telescope provides an angular resolution of ∼32 mas (∼100 km at Io) resolving the Loki Patera emission into two distinct maxima originating from different regions within Loki’s horseshoe lava lake. This observation is consistent with the presence of a high-temperature source observed in previous studies combined with an independent peak arising from cooling crust from recent resurfacing. The deconvolved images also reveal 15 other emission sites on the visible hemisphere of Io including two previously unidentified hot spots.

Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315

The masses, atmospheric makeups, spin–orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small transiting planets are found to have radii 2.23^(+0.30)_(-0.25)R⊕ and 3.95^(+0.42)_(-0.39)R⊕ and orbital periods 9.55 days and 21.06 days, respectively. A radial velocity (RV) trend of 0.3 ± 0.1 m s^(−1) day^(−1) indicates the likely presence of a third body orbiting HD 106315 with period ≳160 days and mass ≳45 M⊕. Transits of this object would have depths ≳0.1% and are definitively ruled out. Although the star has v sin i = 13.2 km s^(−1), it exhibits a short-timescale RV variability of just 6.4 m s^(−1). Thus, it is a good target for RV measurements of the mass and density of the inner two planets and the outer objects orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin–orbit alignment of small planets through the Rossiter–McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study.

Emission from volcanic SO gas on Io at high spectral resolution

Jupiter’s moon Io hosts a dynamic atmosphere that is continually stripped off and replenished through frost sublimation and volcanic outgassing. We observed an emission band at 1.707 µm thought to be produced by hot SO molecules directly ejected from a volcanic vent; the observations were made with the NIRSPEC instrument on the Keck II telescope while Io was in eclipse by Jupiter on three nights in 2012–2016, and included two observations with 10 × higher spectral resolution than all prior observations of this band. These high-resolution spectra permit more complex and realistic modeling, and reveal a contribution to the SO emission from gas reservoirs at both high and low rotational temperatures. The scenario preferred by de Pater et al. (2002) for the source of the SO gas – direct volcanic emission of SO in the excited state – is consistent with these two temperature components if the local gas density is high enough that rotational energy can be lost collisionally before the excited electronic state spontaneously decays. Under this scenario, the required bulk atmospheric gas density and surface pressure are n ∼ 10^(11) cm^(−3) and 1–3 nbar, consistent with observations and modeling of Io’s dayside atmosphere at altitudes below 10 km (Lellouch et al., 2007; Walker et al., 2010). These densities and pressures would be too high for the nightside density if the atmospheric density drops by an order of magnitude or more at night (as predicted by sublimation-supported models), but recent results have shown a drop in SO_2 gas density of only a factor of 5  ±  2 (Tsang et al., 2016). While our observations taken immediately post-ingress and pre-egress (on different dates) prefer models with only a factor of 1.5 change in gas density, a factor of 5 change is still well within uncertainties. In addition, our derived gas densities are for the total bulk atmosphere, while Tsang et al. (2016) specifically measured SO_2. The low-temperature gas component is warmer for observations in the first 20 min of eclipse (in Dec 2015) than after Io had been in shadow for 1.5 h (in May 2016), suggesting cooling of the atmosphere during eclipse. However, individual spectra during the first  ∼ 30 min of eclipse do not show a systematic cooling, indicating that such a cooling would have to take place on a longer timescale than the  ∼ 10 min for cooling of the surface (Tsang et al., 2016). Excess emission is consistently observed at 1.69 µm, which cannot be matched by two-temperature gas models but can be matched by models that over-populate high rotational states. However, a detailed assessment of disequilibrium conditions will require high-resolution spectra that cover both the center of the band and the wing at 1.69 µm. Finally, a comparison of the total band strengths observed across eight dates from 1999 to 2016 reveals no significant dependence on thermal hot spot activity (including Loki Patera), on the time since Io has been in shadow, nor on the phase of Io’s orbit at the time of observation.

Europa’s Optical Aurora

Auroral emissions provide opportunities to study the tenuous atmospheres of solar system satellites, revealing the presence and abundance of molecular and atomic species as well as their spatial and temporal variability. Far-UV aurorae have been used for decades to study the atmospheres of the Galilean satellites. Here we present the first detection of Europas visible-wavelength atomic oxygen aurora at 6300/6364 A arising from the metastable O(^1D) state, observed with the Keck I and Hubble Space Telescope while Europa was in eclipse by Jupiter on six occasions in 2018 February–April. The disk-integrated O(^1D) brightness varies from <500 R up to more than 2 kR between dates, a factor of 15 higher than the O I 1356 A brightness on average. The ratio of emission at 6300/5577 A is diagnostic of the parent molecule; the 5577 A emission was not detected in our data set, which favors O2 as the dominant atmospheric constituent and rules out an O/O_2 mixing ratio above 0.35. For an O_2 atmosphere and typical plasma conditions at Europas orbit, the measured surface brightness range corresponds to column densities of (1–9) × 10^(14) cm^(−2).

OH emission and absorption associated with supernovae in Arp 220

We present parsec-resolution spectral-line VLBI data for two epochs separated by 15 months as a precise new probe of the innermost regions of the nearby Ultraluminous Infrared Galaxy (ULIRG) Arp 220. This galaxy hosts a powerful starburst, with an associated supernova (SN) rate of order 4/yr. An extensive population of compact continuum sources interpreted as radio supernovae (RSNe) and young supernova remnants (SNR) has been imaged. We show here that many of the supernova-related radio continuum point sources exhibit clear evidence of OH absorption or maser emission in the intervening gas, and as such provide us with a sampling of conditions along very narrow and specific lines of sight through the nuclear environment. The OH gas along these lines of sight exhibits velocity dispersions of up to several tens of km/sec, and that in some cases, multiple distinct concentrations of masing gas at different radial velocities can be discerned. There is evidence for variability in the OH properties on ~1yr timescales. Our results are discussed in the context of the overall OH megamaser properties of Arp 220.