Christopher J. Corbally

Debris Disks in Main-Sequence Binary Systems

We observed 69 A3-F8 main-sequence binary star systems using the Multiband Imaging Photometer for Spitzer on board the Spitzer Space Telescope. We find emission significantly in excess of predicted photospheric flux levels for 9 % and 40 % of these systems at 24 and 70 μm, respectively. Twenty-two systems total have excess emission, including four systems that show excess emission at both wavelengths. A very large fraction (nearly 60%) of observed binary systems with small (<3 AU) separations have excess thermal emission. We interpret the observed infrared excesses as thermal emission from dust produced by collisions in planetesimal belts. The incidence of debris disks around main-sequence A3-F8 binaries is marginally higher than that for single old AFGK stars. Whatever combination of nature (birth conditions of binary systems) and nurture (interactions between the two stars) drives the evolution of debris disks in binary systems, it is clear that planetesimal formation is not inhibited to any great degree. We model these dust disks through fitting the spectral energy distributions and derive typical dust temperatures in the range 100-200 K and typical fractional luminosities around 10-5, with both parameters similar to other Spitzer-discovered debris disks. Our calculated dust temperatures suggest that about half the excesses we observe are derived from circumbinary planetesimal belts and around one-third of the excesses clearly suggest circumstellar material. Three systems with excesses have dust in dynamically unstable regions, and we discuss possible scenarios for the origin of this short-lived dust.

The Incidence of λ Boötis Stars via an Extension of the MK Spectral Classification System to Very Young A-Type Stars

In this paper we introduce an extension to the MK system of spectral classification that allows the precise classification of pre–main-sequence (PMS) A-type stars, including most Herbig Ae stars. This classification scheme characterizes the star by a standard MK type, the presence and strength of emission and/or shell lines, and the strength of the Balmer decrement. It can be used to summarize temporal spectral changes in PMS A-type stars, and to search for peculiar types. We have used this scheme to classify 38 Herbig Ae stars as well as 22 PMS stars in the young open clusters NGC 2264, NGC 7160, and IC 348. We have also used this extended system to search for λ Bootis stars among PMS A-type stars. We have found one definite λ Bootis star among the Ae stars, and one marginal λ Bootis star in NGC 2264, yielding statistics not significantly different from those of the λ Bootis stars in the field. This, in addition to other considerations from previous studies, leads us to conclude that the λ Bootis mechanism is operable from very early ages (PMS) to well into the main-sequence life (a few times 108 yr) of only 2%–3% of A-type stars.

Evidence of Halo Microlensing in M31

We have completed an intensive monitoring program of two fields on either side of the center of M31 and report here on the results concerning microlensing of stars in M31. These results stem from a 3 yr study ( the Vatican Advanced Technology Telescope [VATT]/Columbia survey) of microlensing and variability of M31 stars, emphasizing microlensing events of 3 day to 2 month timescales and likely due to masses in M31. These observations were conducted intensively from 1997 to 1999, with baselines 1995 to present, at the VATT and the 1.3 m telescope at MDM Observatory, with additional data from the Isaac Newton Telescope, including about 200 epochs total. The two fields monitored cover 560 arcmin(2) total, positioned along the minor axis on either side of M31. Candidate microlensing events are subject to a number of tests discussed here with the purpose of distinguishing microlensing from variable star activity. A total of four probable microlensing events, when compared with carefully computed event rate and efficiency models, indicate a marginally significant microlensing activity above that expected for the stars alone in M31 ( and the Galaxy) acting as lenses. A maximum likelihood analysis of the distribution of events in timescale and across the face of M31 indicates a microlensing dark matter halo fraction consistent with that seen by MACHO in our Galaxy toward the Large Magellanic Cloud. Specifically, for a nearly singular isothermal sphere model, we find a microlensing halo mass fraction fb = 0.29(-0.13)(+0.30) of the total dark matter and a poorly constrained lensing component mass (0.02 - 1.5 M-.; 1 sigma limits). This study serves as the prototype for a larger study approaching completion; between the two there is significant evidence for an asymmetry in the distribution of microlensing events across the face of M31 and therefore a large population of halo microlensing dark matter objects.

A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters

As part of our continuing search for peculiar A-type stars, especiallyBootis stars, in open clusters of all ages, we have obtained classification spectra of 130 late B, A, and early F-type stars in 12 intermediate-age open clusters, including NGC 1039, 2281, 2548, 6633, 7039, 7063, 7092, and 7209, IC 4665, IC 4756, Stock 2, and Praesepe. The spectra were obtained with resolutions of 1.8 and 3.6 Aon the 0.8 m telescope of Appalachian State University and were classified on the MK system. Numerous classical Ap and Am stars were found among the 130, including two new Ap stars in NGC 7092. In addition, three emission-line stars and two candidateBootis stars were found. Neither of theseBootis candidates turned out to be members of their respective clusters. Combined with 184 stars previously classified in 10 other intermediate-age open clusters, also devoid ofBootis stars, a statistically significant null result is obtained. We discuss the implications of this null result for our understanding of theBootis mechanism.

AN EXPERT COMPUTER PROGRAM FOR CLASSIFYING STARS ON THE MK SPECTRAL CLASSIFICATION SYSTEM

This paper describes an expert computer program (MKCLASS) designed to classify stellar spectra on the MK Spectral Classification system in a way similar to humans—by direct comparison with the MK classification standards. Like an expert human classifier, the program first comes up with a rough spectral type, and then refines that spectral type by direct comparison with MK standards drawn from a standards library. A number of spectral peculiarities, including barium stars, Ap and Am stars, λ Bootis stars, carbon-rich giants, etc., can be detected and classified by the program. The program also evaluates the quality of the delivered spectral type. The program currently is capable of classifying spectra in the violet-green region in either the rectified or flux-calibrated format, although the accuracy of the flux calibration is not important. We report on tests of MKCLASS on spectra classified by human classifiers; those tests suggest that over the entire HR diagram, MKCLASS will classify in the temperature dimension with a precision of 0.6 spectral subclass, and in the luminosity dimension with a precision of about one half of a luminosity class. These results compare well with human classifiers.

The Emotional Brain Hypothesis: Emotional, Social, and Religious Vetting in the Evolution of Rational Decision Making and Scientific Modeling

While sociability has been recognized as a foundation of human evolution and is now well integrated into models of human origins, emotionality has received less attention. It is proposed here, in this preliminary concept paper, that emotionally-informed decision-making developed to the benefit of members of the genus Homo, as an integral part of the evolution of sentience in the hominin line. Emotionality is especially important in the higher expressions of sentience – science, religion, and art – but also in vetting all rational and scientific thought. The authors propose that future researchers in the cognitive science of religion, archaeology, evolutionary psychology, and evolutionary biology incorporate analysis of both emotionality and sociability into their protocols. A brief scenario of early hominin interaction in the search for food is presented, along with a discussion of the emotions involved. In the future, rational decision-making that is vetted by both social and emotional intelligence, as well as religious and ethical precepts, will help to provide solutions to world problems. Emotionality remains critically important for members of the genus Homo as an aspect of their attainment of sentience.

LAMOST observations in the Kepler field

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (lamost) at the Xinglong observatory in China is a new 4-m telescope equipped with 4,000 optical fibers. In 2010, we initiated the lamost-Kepler project. We requested to observe the full field-of-view of the nominal Kepler mission with thelamost to collect low-resolution spectra for as many objects from the KIC 10 catalogue as possible. So far, 12 of the 14 requestedlamost fields have been observed resulting in more than 68,000 low-r esolution spectra. Our preliminary results show that the stellar para meters derived from thelamost spectra are in good agreement with those found in the literature based on high-resolution spectroscopy. Thelamost data allows to distinguish dwarfs from giants and can provide the projected rotational velocity for very fast rotators.

The Asiago-ESO/RASS QSO Survey. II. The Southern Sample*

This is the second paper of a series describing the Asiago-ESO/RASS QSO survey, a project aimed at the construction of an all-sky, statistically well defined sample of very bright QSOs (BJ ≤ 15). Such a survey is required to remove the present uncertainties about the properties of the local QSO population and constitutes an homogeneous database for detailed evolutionary studies of active galactic nuclei (AGNs). We present here the complete southern sample, which comprises 243 bright (12.60 ≤ BJ ≤ 15.13) QSO candidates at high galactic latitudes (|bgal| ≥ 30°). The area covered by the survey is 5660 deg2. Spectroscopy for the 137 still unidentified objects has been obtained. The total number of AGNs turns out to be 111, 63 of which are new identifications. The properties of the selection are discussed. The completeness and the success rate for this survey at the final stage are 63% and 46%, respectively.

The spectra of G dwarf stars towards the galactic poles

Slit spectra of 299 faint, early G dwarf candidates in the directions of the North and South Galactic Poles have been classified on the MK system. An expediency, employing the normal MK standards, was followed to cope with the 40% of stars which proved to have weak-lined spectra. We present these classifications to show what G dwarf stars in the thick disk region of the Galaxy are really like spectroscopically. From the whole spectrum perspective they do resemble the stars of equivalent metallicity in the solar neighborhood. The spectra of several interesting stars are discussed. We also note a tendency for the G-band strength to decrease less fast than the overall line weakening in the metal-weak stars

LAMOST Observations in the Kepler Field. II. Database of the Low-resolution Spectra from the Five-year Regular Survey

The LAMOST-Kepler (LK-) project was initiated to use the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to make spectroscopic follow-up observations for the targets in the field of the Kepler mission. The Kepler field is divided into 14 subfields that are adapted to the LAMOST circular field with a diameter of 5 degrees. During the regular survey phase of LAMOST, the LK-project took data from 2012 June to 2017 June and covered all the 14 subfields at least twice. In particular, we describe in this paper the second Data Release of the LK-project, including all spectra acquired through 2015 May to 2017 June together with the first round observations of the LK-project from 2012 June to 2014 September. The LK-project now counts 227 870 spectra of 156 390 stars, among which we have derived atmospheric parameters (log g, T eff and [Fe/H]) and heliocentric radial velocity (RV) for 173 971 spectra of 126 172 stars. These parameters were obtained with the most recent version of the LAMOST Stellar Parameter Pipeline v 2.9.7. Nearly one half, namely 76 283 targets, are observed both by LAMOST and Kepler telescopes. These spectra, establishing a large spectroscopy library, will be useful for the entire astronomical community, particularly for planetary science and stellar variability on Kepler targets.