Herbig Ae/Be stars (HAeBes) span a key mass range that links low- and high-mass stars, and thus provide an ideal window from which to explore their formation. This paper presents Very Large Telescope/X-shooter spectra of 91 HAeBes, the largest spectroscopic study of HAeBe accretion to date. A homogeneous approach to determining stellar parameters is undertaken for the majority of the sample. Measurements of the ultraviolet are modelled within the context of magnetospheric accretion, allowing a direct determination of mass accretion rates. Multiple correlations are observed across the sample between accretion and stellar properties: the youngest and often most massive stars are the strongest accretors, and there is an almost 1:1 relationship between the accretion luminosity and stellar luminosity. Despite these overall trends of increased accretion rates in HAeBes when compared to classical T Tauri stars, we also find noticeable differences in correlations when considering the Herbig Ae and Herbig Be subsets. This, combined with the difficulty in applying a magnetospheric accretion model to some of the Herbig Be stars, could suggest that another form of accretion may be occurring within Herbig Be mass range.

A spectroscopic survey of Herbig Ae/Be stars with X-shooter – I. Stellar parameters and accretion rates

We obtained spectra in the wavelength range λ = 995-1769 nm of all four known planets orbiting the star HR 8799 Using the suite of instrumentation known as Project 1640 on the Palomar 5 m Hale Telescope, we acquired data at two epochs This allowed for multiple imaging detections of the companions and multiple extractions of low-resolution (R ~ 35) spectra Data reduction employed two different methods of speckle suppression and spectrum extraction, both yielding results that agree The spectra do not directly correspond to those of any known objects, although similarities with L and T dwarfs are present, as well as some characteristics similar to planets such as Saturn We tentatively identify the presence of CH_4 along with NH_3 and/or C_2H_2, and possibly CO_2 or HCN in varying amounts in each component of the system Other studies suggested red colors for these faint companions, and our data confirm those observations Cloudy models, based on previous photometric observations, may provide the best explanation for the new data presented here Notable in our data is that these presumably co-eval objects of similar luminosity have significantly different spectra; the diversity of planets may be greater than previously thought The techniques and methods employed in this paper represent a new capability to observe and rapidly characterize exoplanetary systems in a routine manner over a broad range of planet masses and separations These are the first simultaneous spectroscopic observations of multiple planets in a planetary system other than our own

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Reconnaissance of the hr 8799 exosolar system. i. near-infrared spectroscopy

κ Andromedae is a B9IVn star at 52 pc for which a faint substellar companion separated by 55 ± 2 AU was recently announced. In this work, we present the first spectrum of the companion, "κ And B," using the Project 1640 high-contrast imaging platform. Comparison of our low-resolution YJH-band spectra to empirical brown dwarf spectra suggests an early-L spectral type. Fitting synthetic spectra from PHOENIX model atmospheres to our observed spectrum allows us to constrain the effective temperature to ~2000 K as well as place constraints on the companion surface gravity. Further, we use previously reported log(g) and T_eff measurements of the host star to argue that the κ And system has an isochronal age of 220 ± 100 Myr, older than the 30 Myr age reported previously. This interpretation of an older age is corroborated by the photometric properties of κ And B, which appear to be marginally inconsistent with other 10–100 Myr low-gravity L-dwarfs for the spectral type range we derive. In addition, we use Keck aperture masking interferometry combined with published radial velocity measurements to rule out the existence of any tight stellar companions to κ And A that might be responsible for the system's overluminosity. Further, we show that luminosity enhancements due to a nearly "pole-on" viewing angle coupled with extremely rapid rotation is unlikely. κ And A is thus consistent with its slightly evolved luminosity class (IV), and we propose here that κ And, with a revised age of 220 ± 100 Myr, is an interloper to the 30 Myr Columba association with which it was previously associated. The photometric and spectroscopic evidence for κ And B combined with our reassessment of the system age implies a substellar companion mass of 50^(+16)_(-13) M_Jup, consistent with a brown dwarf rather than a planetary-mass companion.

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The κ Andromedae System: New Constraints on the Companion Mass, System Age, and Further Multiplicity

We investigate the role that planet detection order plays in the Kepler planet detection pipeline. The Kepler pipeline typically detects planets in order of descending signal strength (MES). We find that the detectability of transits experiences an additional $5.5\%$ and $15.9\%$ efficiency loss, for periods $ 200$ days respectively, when detected after the strongest signal transit in a multiple-planet system. We provide a method for determining the transit probability for multiple-planet systems by marginalizing over the empirical Kepler dataset. Furthermore, because detection efficiency appears to be a function of detection order, we discuss the sorting statistics that affect the radius and period distributions of each detection order. Our occurrence rate dataset includes radius measurement updates from the California Kepler Survey (CKS), Gaia DR2, and asteroseismology. Our population model is consistent with the results of Burke et al. (2015), but now includes an improved estimate of the multiplicity distribution. From our obtained model parameters, we find that only $4.0\pm4.6\%$ of solar-like GK dwarfs harbor one planet. This excess is smaller than prior studies and can be well modeled with a modified Poisson distribution, suggesting that the Kepler Dichotomy can be accounted for by including the effects of multiplicity on detection efficiency. Using our modified Poisson model we expect the average number of planets is $5.86\pm0.18$ planets per GK dwarf within the radius and period parameter space of Kepler.

Accounting for incompleteness due to transit multiplicity in Kepler planet occurrence rates

We report extensive new photometry and spectroscopy of the highly variable young stellar object PTF 10nvg (also known as IRAS 20496+4354 and V2492 Cyg), including optical and near-infrared time-series data as well as mid-infrared and millimeter data. Following the previously reported 2010 rise to R_(PTF)≾13^m.5 and subsequent fade, during 2011 and 2012 the source underwent additional episodes of brightening, followed by several magnitude dimming events including prolonged faint states at R_(PTF)≳20^m. The observed high-amplitude variations are largely consistent with extinction changes (ΔA_V up to 30 mag) having a ~220 day quasi-periodic signal. However, photometry measured when the source was near maximum brightness in mid-2010 as well as in late-2012 does not phase well to this period. Spectral evolution includes not only changes in the spectral slope but also correlated variation in the prominence of TiO/VO/CO bands and atomic line emission, as well as anti-correlated variation in forbidden line emission which, along with H_2, dominates optical and infrared spectra at faint epochs. Notably, night-to-night variations in several forbidden doublet strengths and ratios are observed. High-dispersion spectra were obtained in a variety of photometric states and reveal time-variable line profiles. Neutral and singly ionized atomic species are likely formed in an accretion flow and/or impact while the origin of zero-velocity atomic Li I λ6707 in emission is unknown. Forbidden lines, including several rare species, exhibit blueshifted emission profiles and likely arise from an outflow/jet. Several of these lines are also seen spatially offset from the continuum source position, presumably in a shocked region of an extended jet. Blueshifted absorption components of the Na I D doublet, K I λλ7665, 7669 doublet, and the O I 7774 triplet, as well as blueshifted absorption components seen against the broad Hα and Ca II triplet emission lines, similarly are formed in the outflow. CARMA maps resolve on larger scales a spatially extended outflow in millimeter-wavelength CO. We attribute the recently observed photometric and spectroscopic behavior to rotating circumstellar disk material located at separation ɑ ≈ 0.7(M_*/M_☉)^(1/3) AU from the continuum source, causing the semi-periodic dimming. Occultation of the central star as well as the bright inner disk and the accretion/outflow zones renders shocked gas in the inner part of the jet amenable to observation at the faint epochs. We discuss PTF 10nvg as a source exhibiting both accretion-driven (perhaps analogous to V1647 Ori) and extinction-driven (perhaps analogous to UX Ori or GM Cep) high-amplitude variability phenomena.

https://iopscience.iop.org/article/10.1088/0004-6256/145/3/59/pdf

HIGHLY VARIABLE EXTINCTION AND ACCRETION IN THE JET-DRIVING CLASS I-TYPE YOUNG STAR PTF 10nvg (V2492 Cyg, IRAS 20496+4354)

We present adaptive optics photometry and spectra in the JHKL-bands along with high spectral resolution K-band spectroscopy for each component of the Z Canis Majoris system. Our high angular resolution photometry of this very young (<1 Myr) binary, comprised of an FU Ori object and a Herbig Ae/Be star, were gathered shortly after the 2008 outburst while our high resolution spectroscopy was gathered during a quiescent phase. Our photometry conclusively determine that the outburst was due solely to the embedded Herbig Ae/Be member, supporting results from earlier works, and that the optically visible FU Ori component decreased slightly (~30%) in luminosity during the same period, consistent with previous works on the variability of FU Ori type systems. Further, our high-resolution K-band spectra definitively demonstrate that the 2.294 micron CO absorption feature seen in composite spectra of the system is due solely to the FU Ori component, while a prominent CO emission feature at the same wavelength, long suspected to be associated with the innermost regions of a circumstellar accretion disk, can be assigned to the Herbig Ae/Be member. These findings are in contrast to previous analyses (e.g. Malbet et al 2010, Benisty et al. 2010) of this complex system which assigned the CO emission to the FU Ori component.

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High Resolution Infrared Imaging & Spectroscopy of the Z Canis Majoris System During Quiescence & Outburst

The census of young stars near the Sun is incomplete, particularly at lowmasses. Many constituents of the known sample are members of nearby, young moving groups (NYMGs); loose associations of coeval stars with common Galactic kinematics. By mining astrometric and photometric catalogs, new candidates of the young, low-mass star population can be found via their association with NYMGs. We have therefore developed the Cool Astrometrically Selected Targets Optimal For Follow-up Spectroscopy (CASTOFFS ) survey to identify and characterize previously unrecognized 920 The CASTOFFS Survey: High Resolution Optical Spectroscopy of Bright Targets young, low-mass stars. We combine astrometry, photometry, and activity to identify candidates and use dedicated spectroscopic follow-up to verify their youth and group kinematics. We are now 2 years into CASTOFFS and present preliminary results from spectroscopic follow-up of 62 targets with V ≤ 14. Our results reveal many high probability members of NYMGs, young field stars, and new wide, visual, and spectroscopic binaries.

Adam Kraus

Papers

High Resolution Infrared Imaging & Spectroscopy of the Z Canis Majoris System During Quiescence & Outburst

The CASTOFFS Survey: High Resolution Optical Spectroscopy of Bright Targets