Studies of bright A-type stars : Second part

As a continuation of a paper presented at the 14th meeting of the Association, the colors, spectral types, rotational velocities and photometric narrow-band indices of the A-type stars from paper I, are discussed. An analysis of the data permits to obtain the dispersion of each of these parameters. The importance of these dispersions for the treatment of interstellar absorption and blanketing corrections is stressed. The paper in full will be published elsewhere.Asociación Argentina de Astronomí

Studies of bright A-type stars : Second part

As a continuation of a paper presented at the 14th meeting of the Association, the colors, spectral types, rotational velocities and photometric narrow-band indices of the A-type stars from paper I, are discussed. An analysis of the data permits to obtain the dispersion of each of these parameters. The importance of these dispersions for the treatment of interstellar absorption and blanketing corrections is stressed. The paper in full will be published elsewhere.Asociación Argentina de Astronomí

The luminosity function obtained from bright stars

As a preliminary step to derive the luminosity function the underlying hypothesis involved in the mean absolute magnitudes method have been analyzed. The study of the material published by Cowley, A. P., Hiltner, W. A. and Witt, A. N. (A.J., 72, 1334, 1967) shows that the hypothesis of a linear relationship between the mean absolute magnitude and H, as well as the hypothesis that such a relationship does not depend on the apparent magnitude, have little influence on the obtained values. The shape of the luminosity function is not biased either by the adopted shape of the relative distribution function of absolute magnitudes for each H, but it depends critically on the number of stars in each magnitude and proper motion interval.Asociación Argentina de Astronomí

The luminosity function obtained from bright stars

As a preliminary step to derive the luminosity function the underlying hypothesis involved in the mean absolute magnitudes method have been analyzed. The study of the material published by Cowley, A. P., Hiltner, W. A. and Witt, A. N. (A.J., 72, 1334, 1967) shows that the hypothesis of a linear relationship between the mean absolute magnitude and H, as well as the hypothesis that such a relationship does not depend on the apparent magnitude, have little influence on the obtained values. The shape of the luminosity function is not biased either by the adopted shape of the relative distribution function of absolute magnitudes for each H, but it depends critically on the number of stars in each magnitude and proper motion interval.Asociación Argentina de Astronomí

A GLIMPSE into the Nature of Galactic Mid-IR Excesses

We investigate the nature of the mid-IR excess for 31 intermediate-mass stars that exhibit an 8 micron excess in either the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire or the Mid-Course Space Experiment using high resolution optical spectra to identify stars surrounded by warm circumstellar dust. From these data we determine projected stellar rotational velocities and estimate stellar effective temperatures for the sample. We estimate stellar ages from these temperatures, parallactic distances, and evolutionary models. Using MIPS [24] measurements and stellar parameters we determine the nature of the infrared excess for 19 GLIMPSE stars. We find that 15 stars exhibit Halpha emission and four exhibit Halpha absorption. Assuming that the mid-IR excesses arise in circumstellar disks, we use the Halpha fluxes to model and estimate the relative contributions of dust and free-free emission. Six stars exhibit Halpha fluxes that imply free-free emission can plausibly explain the infrared excess at [24]. These stars are candidate classical Be stars. Nine stars exhibit Halpha emission, but their Halpha fluxes are insufficient to explain the infrared excesses at [24], suggesting the presence of a circumstellar dust component. After the removal of the free-free component in these sources, we determine probable disk dust temperatures of Tdisk~300-800 K and fractional infrared luminosities of L(IR)/L(*)~10^-3. These nine stars may be pre-main-sequence stars with transitional disks undergoing disk clearing. Three of the four sources showing Halpha absorption exhibit circumstellar disk temperatures ~300-400 K, L(IR)/L(*)~10^-3, IR colors K-[24]< 3.3, and are warm debris disk candidates. One of the four Halpha absorption sources has K-[24]> 3.3 implying an optically thick outer disk and is a transition disk candidate.Comment: 17 figures. Accepted for publication in Ap

The Circumstellar Disk of HD 141569 Imaged with NICMOS

Coronagraphic imaging with the Near Infrared Camera and Multi Object Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'') radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected light image at 1.1 micron shows the disk oriented at a position angle of 356 +/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic scattering function of the dust in the disk makes the side inclined toward us, the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from the star and falls off to both larger and smaller radii. A region of depleted material, or a gap, in the disk is centered 250 AU from the star. The dynamical effect of one or more planets may be necessary to explain this morphology.Comment: 4 pages, LaTeX with emulateapj.sty and epsfig.sty, 4 postscript figures, Accepted to ApJ Letter

Transition Properties of Low Lying States in Atomic Indium

We present here the results of our relativistic many-body calculations of various properties of the first six low-lying excited states of indium. The calculations were performed using the relativistic coupled-cluster method in the framework of the singles, doubles and partial triples approximation. We obtain a large lifetime ~10s for the [4p^6]5s^2 5p_{3/2} state, which had not been known earlier. Our precise results could be used to shed light on the reliability of the lifetime measurements of the excited states of atomic indium that we have considered in the present work.Comment: 6 pages, 1 figure and 3 table

The DDO IVC Distance Project: Survey Description and the Distance to G139.6+47.6

We present a detailed analysis of the distance determination for one intermediate Velocity Cloud (IVC G139.6+47.6) from the ongoing DDO IVC Distance Project. Stars along the line of sight to G139.6+47.6 are examined for the presence of sodium absorption attributable to the cloud, and the distance bracket is established by astrometric and spectroscopic parallax measurements of demonstrated foreground and background stars. We detail our strategy regarding target selection, observational setup, and analysis of the data, including a discussion of wavelength calibration and sky subtraction uncertainties. We find a distance estimate of 129 (+/- 10) pc for the lower limit and 257 (+211-33) pc for the upper limit. Given the high number of stars showing absorption due to this IVC, we also discuss the small-scale covering factor of the cloud and the likely significance of non-detections for subsequent observations of this and other similar IVC's. Distance measurements of the remaining targets in the DDO IVC project will be detailed in a companion paper.Comment: 10 pages, 6 figures, LaTe

Systematic motions in the Galactic plane found in the Hipparcos Catalogue using Herschel's Method

Two motions in the galactic plane have been detected and characterized, based on the determination of a common systematic component in Hipparcos catalogue proper motions. The procedure is based only on positions, proper motions and parallaxes, plus a special algorithm which is able to reveal systematic trends. Our results come from two stellar samples. Sample 1 has 4566 stars and defines a motion of apex (l,b)=(177.8,3.7)+/-(1.5,1.0) and space velocity V=27+/-1 km/s. Sample 2 has 4083 stars and defines a motion of apex (l,b)=(5.4,-0.6)+/-(1.9,1.1) and space velocity V=32+/-2 km/s. Both groups are distributed all over the sky and cover a large variety of spectral types, which means that they do not belong to a specific stellar population. Herschel's method is used to define the initial samples of stars and later to compute the common space velocity. The intermediate process is based on the use of a special algorithm to determine systematic components in the proper motions. As an important contribution, this paper sets out a new way to study the kinematics of the solar neighborhood, in the search for streams, associations, clusters and any other space motion shared by a large number of stars, without being restricted by the availability of radial velocities.Comment: 12 pages and 12 eps figures. LaTe

Mysterious Murder - MCTS-driven murder mystery generation

© 2019 IEEE. We present an approach to procedurally generate the narrative of a simple murder mystery. As a basis for the simulation, we use a rule evaluation system inspired by Ceptre, which employs linear logic to resolve valid actions during each step of the simulation. We extend Ceptre's system with a concept of believable agents to make consecutive actions appear to have a causal connection so that players can comprehend the flow of events. The parts of the generated narratives are then presented to a player whose task it is to figure out who the murderer in this story could have been. Rather than aiming to replace highly authored narratives, this project generates puzzles, which may contain emerging arcs of a story as perceived by the player. While we found that even a simple rule set can create stories that are interesting to reason about, we expect that this type of system is flexible enough to create considerably more engaging stories if enough time is invested in authoring more complex rule sets