[en] We present analytic estimates of the fractional uncertainties on the mass, radius, surface gravity, and density of a transiting planet, using only empirical or semi-empirical measurements. We first express these parameters in terms of transit photometry and radial velocity (RV) observables, as well as the stellar radius R _⋆, if required. In agreement with previous results, we find that, assuming a circular orbit, the surface gravity of the planet (g _p) depends only on empirical transit and RV parameters, namely the planet period P, the transit depth δ, the RV semi-amplitude K _⋆, the transit duration T, and the ingress/egress duration τ. However, the planet mass and density depend on all these quantities, plus R _⋆. Thus, an inference about the planet mass, radius, and density must rely upon an external constraint such as the stellar radius. For bright stars, stellar radii can now be measured nearly empirically by using measurements of the stellar bolometric flux, the effective temperature, and the distance to the star via its parallax, with the extinction A _V being the only free parameter. For any given system, there is a hierarchy of achievable precisions on the planetary parameters, such that the planetary surface gravity is more accurately measured than the density, which in turn is more accurately measured than the mass. We find that surface gravity provides a strong constraint on the core mass fraction of terrestrial planets. This is useful, given that the surface gravity may be one of the best measured properties of a terrestrial planet.

[en] As many as 10% of OB-type stars have global magnetic fields, which is surprising given that their internal structure is radiative near the surface. A direct probe of internal structure is pulsations, and some OB-type stars exhibit pressure modes (β Cep pulsators) or gravity modes (slowly pulsating B-type stars; SPBs); a few rare cases of hybrid β Cep/SPBs occupy a narrow instability strip in the H-R diagram. The most precise fundamental properties of stars are obtained from eclipsing binaries (EBs), and those in clusters with known ages and metallicities provide the most stringent constraints on theory. Here we report the discovery that HD 149834 in the ∼5 Myr cluster NGC 6193 is an EB comprising a hybrid β Cep/SPB pulsator and a highly irradiated low-mass companion. We determine the masses, radii, and temperatures of both stars; the ∼9.7 M _⊙ primary resides in the instability strip where hybrid pulsations are theoretically predicted. The presence of both SPB and β Cep pulsations indicates that the system has a near-solar metallicity, and is in the second half of the main-sequence lifetime. The radius of the ∼1.2 M _⊙ companion is consistent with theoretical pre-main-sequence isochrones at 5 Myr, but its temperature is much higher than expected, perhaps due to irradiation by the primary. The radius of the primary is larger than expected, unless its metallicity is super-solar. Finally, the light curve shows residual modulation consistent with the rotation of the primary, and Chandra observations reveal a flare, both of which suggest the presence of starspots and thus magnetism on the primary.

[en] We report new spectroscopic and photometric observations of the main-sequence, detached, eccentric, double-lined eclipsing binary V541 Cyg (P = 15.34 days, e = 0.468). Using these observations together with existing measurements, we determine the component masses and radii to better than 1% precision: $M_1={2.335}_{-<!--\; ???\; -->0.013}^{+0.017}{M}_{\odot <!--\; ???\; -->}$, $M_2={2.260}_{-<!--\; ???\; -->0.013}^{+0.016}{M}_{\odot <!--\; ???\; -->}$, $R_1={1.859}_{-<!--\; ???\; -->0.009}^{+0.012}{R}_{\odot <!--\; ???\; -->}$, and $R_2={1.808}_{-<!--\; ???\; -->0.013}^{+0.015}{R}_{\odot <!--\; ???\; -->}$. The nearly identical B9.5 stars have estimated effective temperatures of 10650 ± 200 K and 10350 ± 200 K. A comparison of these properties with current stellar evolution models shows excellent agreement at an age of about 190 Myr and [Fe/H] ≈ −0.18. Both components are found to be rotating at the pseudo-synchronous rate. The system displays a slow periastron advance that is dominated by general relativity (GR), and has previously been claimed to be slower than predicted by theory. Our new measurement, $\stackrel{\dot{}<!--\; ??\; -->}{\mathrm{\omega <!--\; ??\; -->}}={0.859}_{-<!--\; ???\; -->0.017}^{+0.042}$ deg century⁻¹, has an 88% contribution from GR and agrees with the expected rate within the uncertainties. We also clarify the use of the gravity darkening coefficients in the light-curve fitting Eclipsing Binary Orbit Program (EBOP), a version of which we use here.

[en] Be stars have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform a comprehensive analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, a baseline of up to 10 years, photometric precision of about 1%, and coverage of about 60% of the sky. We analyze KELT light curves of 610 known Be stars in both the northern and southern hemispheres in an effort to study their variability. Consistent with other studies of Be star variability, we find most of the stars to be photometrically variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsations (25%), outbursts (36%), and long-term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-types. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.

[en] We present TYC 2505-672-1 as a newly discovered and remarkable eclipsing system comprising an M-type red giant that undergoes a ∼3.45 year long, near-total eclipse (depth of ∼4.5 mag) with a very long period of ∼69.1 years. TYC 2505-672-1 is now the longest-period eclipsing binary system yet discovered, more than twice as long as that of the currently longest-period system, ϵ Aurigae. We show from analysis of the light curve including both our own data and historical data spanning more than 120 years and from modeling of the spectral energy distribution, both before and during eclipse, that the red giant primary is orbited by a moderately hot source ( T _eff ≈ 8000 K) that is itself surrounded by an extended, opaque circumstellar disk. From the measured ratio of luminosities, the radius of the hot companion must be in the range of 0.1–0.5 R _⊙ (depending on the assumed radius of the red giant primary), which is an order of magnitude smaller than that for a main sequence A star and 1–2 orders of magnitude larger than that for a white dwarf. The companion is therefore most likely a “stripped red giant” subdwarf-B type star destined to become a He white dwarf. It is, however, somewhat cooler than most sdB stars, implying a very low mass for this “pre-He-WD” star. The opaque disk surrounding this hot source may be a remnant of the stripping of its former hydrogen envelope. However, it is puzzling how this object became stripped, given that it is at present so distant (orbital semimajor axis of ∼24 au) from the current red giant primary star. Extrapolating from our calculated ephemeris, the next eclipse should begin in early UT 2080 April and end in mid UT 2083 September (eclipse center UT 2081 December 24). In the meantime, radial velocity observations would establish the masses of the components, and high-cadence UV observations could potentially reveal oscillations of the hot companion that would further constrain its evolutionary status. In any case, this system is poised to become an exemplar of a very rare class of systems, even more extreme in several respects than the well studied archetype ϵ Aurigae.

[en] Using the Spitzer Space Telescope, we observed a transit at 3.6 μm of KELT-11b. We also observed three partial planetary transits from the ground. We simultaneously fit these observations, ground-based photometry from Pepper et al., radial velocity data from Pepper et al., and a spectral energy distribution (SED) model using catalog magnitudes and the Hipparcos parallax to the system. The only significant difference between our results and those of Pepper et al. is that we find the orbital period to be shorter by 37 s, 4.73610 ± 0.00003 versus 4.73653 ± 0.00006 days, and we measure a transit center time of ${\mathrm{B}\mathrm{J}\mathrm{D}}_{\mathrm{T}\mathrm{D}\mathrm{B}}$ 2457483.4310 ± 0.0007, which is 42 minutes earlier than predicted. Using our new photometry, we precisely measure the density of the star KELT-11 to 4%. By combining the parallax and catalog magnitudes of the system, we are able to measure the radius of KELT-11b essentially empirically. Coupled with the stellar density, this gives a parallactic mass and radius of 1.8 $M_{\odot <!--\; ???\; -->}$ and 2.9 $R_{\odot <!--\; ???\; -->}$, which are each approximately 1σ higher than the adopted model-estimated mass and radius. If we conduct the same fit using the expected parallax uncertainty from the final Gaia data release, this difference increases to 4σ. The differences between the model and parallactic masses and radii for KELT-11 demonstrate the role that precise Gaia parallaxes, coupled with simultaneous photometric, radial velocity, and SED fitting, can play in determining stellar and planetary parameters. With high-precision photometry of transiting planets and high-precision Gaia parallaxes, the parallactic mass and radius uncertainties of stars become 1% and 3%, respectively. TESS is expected to discover 60–80 systems where these measurements will be possible. These parallactic mass and radius measurements have uncertainties small enough that they may provide observational input into the stellar models themselves.

[en] We present the discovery of two extended ∼0.12 mag dimming events of the weak-lined T Tauri star V1334. The start of the first event was missed but came to an end in late 2003, and the second began in 2009 February, and continues as of 2016 November. Since the egress of the current event has not yet been observed, it suggests a period of >13 years if this event is periodic. Spectroscopic observations suggest the presence of a small inner disk, although the spectral energy distribution shows no infrared excess. We explore the possibility that the dimming events are caused by an orbiting body (e.g., a disk warp or dust trap), enhanced disk winds, hydrodynamical fluctuations of the inner disk, or a significant increase in the magnetic field flux at the surface of the star. We also find a ∼0.32 day periodic photometric signal that persists throughout the 2009 dimming which appears to not be due to ellipsoidal variations from a close stellar companion. High-precision photometric observations of V1334 Tau during K2 campaign 13, combined with simultaneous photometric and spectroscopic observations from the ground, will provide crucial information about the photometric variability and its origin.

[en] One of the most well-studied young stellar associations, Taurus–Auriga, was observed by the extended Kepler mission, K2 , in the spring of 2017. K2 Campaign 13 (C13) is a unique opportunity to study many stars in this young association at high photometric precision and cadence. Using observations from the Kilodegree Extremely Little Telescope (KELT) survey, we identify “dippers,” aperiodic and periodic variables among K2 C13 target stars. This release of the KELT data (light curve data in e-tables) provides the community with long-time baseline observations to assist in the understanding of the more exotic variables in the association. Transient-like phenomena on timescales of months to years are known characteristics in the light curves of young stellar objects, making contextual pre- and post- K2 observations critical to understanding their underlying processes. We are providing a comprehensive set of the KELT light curves for known Taurus–Auriga stars in K2 C13. The combined data sets from K2 and KELT should permit a broad array of investigations related to star formation, stellar variability, and protoplanetary environments.

[en] We present the discovery of a hot Jupiter transiting the V = 9.23 mag main-sequence A-star KELT-17 (BD+14 1881). KELT-17b is a ${1.31}_{-<!--\; ???\; -->0.29}^{+0.28}{M}_{\mathrm{J}}$, ${1.525}_{-<!--\; ???\; -->0.060}^{+0.065}{R}_{\mathrm{J}}$ hot-Jupiter in a 3.08-day period orbit misaligned at −115.°9 ± 4.°1 to the rotation axis of the star. The planet is confirmed via both the detection of the radial velocity orbit, and the Doppler tomographic detection of the shadow of the planet during two transits. The nature of the spin–orbit misaligned transit geometry allows us to place a constraint on the level of differential rotation in the host star; we find that KELT-17 is consistent with both rigid-body rotation and solar differential rotation rates ($\mathrm{\alpha <!--\; ??\; -->}<<!--\; <\; -->0.30$ at $2\mathrm{\sigma <!--\; ??\; -->}$ significance). KELT-17 is only the fourth A-star with a confirmed transiting planet, and with a mass of ${1.635}_{-<!--\; ???\; -->0.061}^{+0.066}{M}_{\odot <!--\; ???\; -->}$, an effective temperature of 7454 ± 49 K, and a projected rotational velocity of $v\sin I_{\ast <!--\; ???\; -->}={44.2}_{-<!--\; ???\; -->1.3}^{+1.5}\mathrm{k}\mathrm{m}{\mathrm{s}}^{-<!--\; ???\; -->1};$ it is among the most massive, hottest, and most rapidly rotating of known planet hosts.

[en] We present the discovery of two planets orbiting the nearby (D = 11.9 pc) K7 dwarf Gl 414A. Gl 414A b is a sub-Neptune mass planet with $M_b\sin i_b={7.60}_{-<!--\; ???\; -->2.19}^{+2.44}$ M _⊕ and a semimajor axis of 0.23 ± 0.01 au. Gl 414A c is a sub-Saturn mass planet with $M_c\sin i_c={53.83}_{-<!--\; ???\; -->8.58}^{+9.18}$ M _⊕ and a semimajor axis of 1.43 ± 0.06 au. We jointly analyzed radial velocity data from Keck/HIRES and the Automated Planet Finder at Lick Observatory, as well as photometric data from KELT, to detect the two planets and two additional signals related to the rotationally modulated activity and the long-term magnetic activity cycle of the star. The outer planet in this system may be a potential candidate for future direct-imaging missions.