Element-by-element we have combined the optical components in the three 2MASS cameras, and incorporated detector quantum efficiency curves and site-specific atmospheric transmissions, to create three relative spectral response curves (RSRs). We provide absolute 2MASS attributes associated with "zero magnitude" in the JHKs bands so that these RSRs may be used for synthetic photometry. The RSRs tie 2MASS to the Cohen-Walker-Witteborn framework of absolute photometry and spectra for the purpose of using 2MASS data to support the development of absolute calibrators for IRAC and pairwise cross-calibrators between all three SIRTF instruments. We examine the robustness of these RSRs to changes in water vapor within a night. We compare the observed 2MASS magnitudes of 33 stars (converted from the precision optical calibrators of Landolt and Carter-Meadows into absolute infrared calibrators from 1.2-35 um with our predictions, thereby deriving 2MASS "zero point offsets" from the ensemble. These offsets are the final ingredients essential to merge 2MASS $JHK_{s}$ data with other absolutely calibrated bands and stellar spectra, and to support the creation of faint calibration stars for SIRTF.

Spectral Irradiance Calibration in the Infrared. XIV: the Absolute Calibration of 2MASS

The precision of photometric and spectroscopic observations has been systematically improved in the last decade, mostly thanks to space-borne photometric missions and ground-based spectrographs dedicated to finding exoplanets. The field of eclipsing binary stars strongly benefited from this development. Eclipsing binaries serve as critical tools for determining fundamental stellar properties (masses, radii, temperatures, and luminosities), yet the models are not capable of reproducing observed data well, either because of the missing physics or because of insufficient precision. This led to a predicament where radiative and dynamical effects, insofar buried in noise, started showing up routinely in the data, but were not accounted for in the models. PHOEBE (PHysics Of Eclipsing BinariEs; http://phoebe-project.org) is an open source modeling code for computing theoretical light and radial velocity curves that addresses both problems by incorporating missing physics and by increasing the computational fidelity. In particular, we discuss triangulation as a superior surface discretization algorithm, meshing of rotating single stars, light travel time effects, advanced phase computation, volume conservation in eccentric orbits, and improved computation of local intensity across the stellar surfaces that includes the photon-weighted mode, the enhanced limb darkening treatment, the better reflection treatment, and Doppler boosting. Here we present the concepts on which PHOEBE is built and proofs of concept that demonstrate the increased model fidelity.

https://iopscience.iop.org/article/10.3847/1538-4365/227/2/29/pdf

Physics of eclipsing binaries. ii. toward the increased model fidelity

Direct detection of thermal emission from nearby hot Jupiters has greatly advanced our knowledge of extrasolar planets in recent years. Since hot Jupiter systems can be regarded as analogs of high-contrast binaries, ground-based infrared long-baseline interferometers have the potential to resolve them and detect their thermal emission with precision closure phase—a method that is immune to the systematic errors induced by the Earth's atmosphere. In this work, we present closure-phase studies toward direct detection of nearby hot Jupiters using the CHARA interferometer array outfitted with the MIRC instrument. We carry out closure-phase simulations and conduct a large number of observations for the best candidate υ And. Our experiments suggest that the method is feasible with highly stable and precise closure phases. However, we also find much larger systematic errors than expected in the observations, most likely caused by dispersion across different wavelengths. We find that using higher spectral resolution modes (e.g., R ¼ 150) can significantly reduce the systematics. By combining all cali- brators in an observing run together, we are able to roughly recalibrate the lower spectral resolution data, allowing us to obtain upper limits of the star-planet contrast ratios of υ And b across the H band. The data also allow us to get a refined stellar radius of 1:625 � 0:011 R⊙. Our best upper limit corresponds to a contrast ratio of 2:1 × 10 3 :1 with 90% confidence level at 1.52 μm, suggesting that we are starting to have the capability of constraining atmospheric models of hot Jupiters with interferometry. With recent and upcoming improvements of CHARA/MIRC, the pros- pect of detecting emission from hot Jupiters with closure phases is promising.

Toward Direct Detection of Hot Jupiters with Precision Closure Phase

We examine high-cadence space photometry taken by the Transiting Exoplanet Survey Satellite (TESS) of a sample of evolved massive stars (26 Wolf-Rayet stars and 8 Luminous Blue Variables or candidate LBVs). To avoid confusion problems, only stars without bright Gaia neighbours and without evidence of bound companions are considered. This leads to a clean sample, whose variability properties should truly reflect the properties of the WR and LBV classes. Red noise is detected in all cases and its fitting reveals characteristics very similar to those found for OB-stars. Coherent variability is also detected for 20% of the WR sample. Most detections occur at moderately high frequency (3--14/d), hence are most probably linked to pulsational activity. This work doubles the number of WRs known to exhibit high-frequency signals.

/pdf/red-noise-and-pulsations-in-evolved-massive-stars-2nhfmplx13.pdf

Red noise and pulsations in evolved massive stars

Context. MWC?314 is one of the most luminous stars in the Milky Way. Its fundamental parameters are similar to those of luminous blue variables (LBVs), although no large photometric variations have been recorded. Moreover, it shows no evidence of either a dust shell or a relevant spectral variability.Aims. The main purpose of this work is to clarify the origin of the radial velocity and line profile variations exhibited by absorption and emission lines.Methods. We analyzed the radial velocity (RV) variations displayed by the absorption lines from the star’s atmosphere using high-resolution optical spectra and fitting the RV curve with an eccentric orbit model. We also studied the RV and profile variations of some permitted and forbidden emission lines of metallic ions with a simple geometric model. The behavior of the Balmer and He?i lines has also been investigated.Results. Fourier analysis applied to the RV of the absorption lines clearly shows a 60-day periodicity. A dense coverage of the RV curve allowed us to derive accurate orbital parameters. The RV of the Fe?ii emission lines varies in the same way, but with a smaller amplitude. Additionally, the intensity ratio of the blue/red peaks of these emission lines correlates with the RV variations. The first three members of the Balmer series as well as [N?ii] lines display a nearly constant RV and no profile variations in phase with the orbital motion instead. The He?i??5876 A line shows a strongly variable profile with broad and blue-shifted absorption components that reach velocities of =-1000 km?s-1 in some specific orbital phases.Conclusions. Our data and analysis provide strong evidence that the object is a binary system composed of a supergiant B[e] star and an undetected companion. The emission lines with a non-variable RV could originate in a circumbinary region. For the Fe?ii emission lines, we propose a simple geometrical two-component model where a compact source of Fe?ii emission, moving around the center of mass, is affected by a static extra absorption that originates from a larger area. Finally, the blue-shifted absorption in the He?i??5876 A line could be the result of density enhancements in the primary star wind that is flowing towards the companion, and which is best observed when projected over the disk of the primary star.

https://www.aanda.org/articles/aa/pdf/2016/01/aa27022-15.pdf

Interpreting the spectral behavior of MWC 314

MWC 314 is a bright candidate luminous blue variable (LBV) that resides in a fairly close binary system, with an orbital period of 60.753 ± 0.003?d. We observed MWC 314 with a combination of optical spectroscopy, broad-band ground- and space-based photometry, as well as with long baseline, near-infrared interferometry. We have revised the single-lined spectroscopic orbit and explored the photometric variability. The orbital light curve displays two minima each orbit that can be partially explained in terms of the tidal distortion of the primary that occurs around the time of periastron. The emission lines in the system are often double-peaked and stationary in their kinematics, indicative of a circumbinary disc. We find that the stellar wind or circumbinary disc is partially resolved in the K'-band with the longest baselines of the CHARA Array. From this analysis, we provide a simple, qualitative model in an attempt to explain the observations. From the assumption of Roche Lobe overflow and tidal synchronization at periastron, we estimate the component masses to be M1 ˜ 5?M? and M2 ˜ 15?M?, which indicates a mass of the LBV that is extremely low. In addition to the orbital modulation, we discovered two pulsational modes with the MOST satellite. These modes are easily supported by a low-mass hydrogen-poor star, but cannot be easily supported by a star with the parameters of an LBV. The combination of these results provides evidence that the primary star was likely never a normal LBV, but rather is the product of binary interactions. As such, this system presents opportunities for studying mass-transfer and binary evolution with many observational techniques.

Spectroscopy, MOST Photometry, and Interferometry of MWC 314: Is it an LBV or an interacting binary?

We initiated a multi-technique campaign to understand the physics an d properties of the massive binary systemMWC 314. Our observations included optical high-resolution spectr oscopy and Johnson photometry, near-infrared spectrophotometry, and K 0 band long-baseline interferometry with the CHARA Array. Our resu ltsplace strong constraints on the spectroscopic orbit, along with re asonable observations of the phase-lockedphotometric variability. Our interferometry, with input from the sp ectrophotometry, provides information onthe geometry of the system that appears to consist of a primary s tar lling its Roche Lobe and loosing massboth onto a hidden companion and through the outer Lagrangian po int, feeding a circumbinary disk. While themulti-faceted observing program is allowing us to place some constra ints on the system, there is also a possibilitythat the outow seen by CHARA is actually a jet and not a circumbinar y disk.Keywords: stars: early-type { binaries: close { stars: individual (MWC 314) { m ethods: observational {techniques: high angular resolution, spectroscopic

MWC 314: binary results from optical interferometry compared with spectroscopy and photometry

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Spectroscopy, MOST Photometry, and Interferometry of MWC 314: Is it an LBV or an interacting binary?

MWC 314: binary results from optical interferometry compared with spectroscopy and photometry