Alan D. Welty

Optical excess emission in T Tauri stars

We present a set of simultaneous high-resolution spectroscopic and spectrophotometric observations of 22 K7-M1 T Tauri stars in the Taurus-Auriga dark cloud. Analysis of the high-resolution data makes it possible to separate the optical excess (veiling) emission from the photospheric fluxes in these stars. The amount of optical excess emission at 5500 A ranges from undetectable (≤10% of the photosphere) to as much as 10 times the photospheric flux in the most extreme objects

Hubble Space Telescope Observations of the Middle-aged Pulsar 0656+14

Multiwavelength spectral observations of middle-aged (τ~104-106 yr) isolated pulsars enable one in principle to separate thermal radiation emitted from the neutron star surface and nonthermal radiation from its magnetosphere. We have previously detected the middle-aged radio and soft X-ray pulsar 0656+14 with the Hubble Space Telescope Faint Object Camera (FOC) long-pass filter F130LP. In the present Letter we report new FOC observations of this pulsar with three broadband filters: F430W, F342W, and F195W. The optical-UV spectral flux can be fitted with a two-component spectral model that combines a power-law spectrum with a Rayleigh-Jeans spectrum. The nonthermal component with the power-law index α=1.4−0.7+ 0.6 dominates at λ3000 A. The thermal component is characterized by the Rayleigh-Jeans parameter, G ≡ T6(R10/d500)2, where T=106T6 K is the brightness temperature, R=10R10 km is the neutron star radius as seen by a distant observer, and d=500d500 pc is the distance. For a plausible extinction, E(B-V)=0.03, we obtained G=3.6+ 1.6−2.0. The observed shape of the optical-UV spectrum of PSR 0656+14 differs drastically from those of both younger pulsars (Crab, 0540-69, Vela) and the older pulsar Geminga.

The reduction of fiber-fed echelle spectrograph data: Methods and an IDL-based solution procedure

Echelle spectrograph data present several challenges in data reduction. In this paper we address the general problem of accurately extracting spectra from a nights worth of raw CCD fiber-fed echelle data frames. We first briefly review echelle spectroscopy: properties of the basic echelle spectrograph, how the orders are arranged on the CCD, and what demands and constraints this data format places on reduction algorithms. We then discuss solutions to the various problems for fiber-fed data, with particular emphasison the removal of the scattered light background. Finally, we discuss our implementation of these solutions. We have written a package using the Interactive Data Language (IDL) that uses the methods described in this paper to give accurate extractions of spectra from fiber-fed echelle frames with any number of spectral orders of arbitrary tilt and curvature. We describe how interested persons may obtain the package through anonymous FTP.

Library of Medium-Resolution Fiber Optic Echelle Spectra of F, G, K, and M Field Dwarfs to Giant Stars

We present a library of Penn State Fiber Optic Echelle (FOE) observations of a sample of —eld stars with spectral types F to M and luminosity classes V to I. The spectral coverage is from 3800 to 10000 Ae with a nominal resolving power of 12,000. These spectra include many of the spectral lines most widely used as optical and near-infrared indicators of chromospheric activity such as the Balmer lines (Ha to Hv), Ca II H & K, the Mg I b triplet, Na I He I and Ca II IRT lines. There are also a large D 1 ,D 2 ,D 3 , number of photospheric lines, which can also be aUected by chromospheric activity, and temperature- sensitive photospheric features such as TiO bands. The spectra have been compiled with the goal of providing a set of standards observed at medium resolution. We have extensively used such data for the study of active chromosphere stars by applying a spectral subtraction technique. However, the data set presented here can also be utilized in a wide variety of ways ranging from radial velocity templates to study of variable stars and stellar population synthesis. This library can also be used for spectral classi- —cation purposes and determination of atmospheric parameters log g, (Fe/H)). A digital version of (T eff , all the fully reduced spectra is available via ftp and the World Wide Web (WWW) in FITS format. Subject headings: atlasesstars: activitystars: chromospheresstars: late-type

Optical spectroscopy of Z Canis Majoris, V1057 Cygni, and FU Orionis - Accretion disks and signatures of disk winds

High resolution, high SNR optical spectra have been used to investigate the hypothesis that in outburst, FU Ori objects are self-luminous accretion disks whose light dominates at optical and near-IR wavelengths. Strong evidence has been found for linewidth versus wavelength correlation in good agreement with model predictions for Z CMa and V1057 Cyg, but not for FU Ori itself. Linewidth varies continuously with wavelength at optical wavelengths in the former two objects, In the case of FU Ori, it is argued that a combination of strong wind components to spectral lines, and surface gravity possibly being lower than that of supergiants, conceals the underlying linewidth versus wavelength relationship. A marginal correlation is found between linewidth and lower excitation potential in all three objects. Synthetic disk spectra are subtracted from observed spectral, and remarkably good fits are found for all three objects for wavelengths longer than about 5000 A.

The distribution of maser emission in OH/IR stars

The 1612 MHz OH emission from five OH/IR stars has been mapped at three epochs over a 2.5 yr period of time. Although the stars were observed at very different phases in the radio light curve of each, there were no remarkable changes in the appearance of the maps. This probably implies that the properties of the masers do not range widely throughout a maser shell. The maps have been used to produce star-centered surface maps of the distribution of maser emission from each star. The surface maps generally are sparsely filled with OH emission and are dominated by relatively few (about 10) major clumps of emission. The presence of large regions of low intensity in the surface maps suggests that the number of individual emitting elements is relatively small or that there are a larger number of elements which are distributed in the shell in a distinctly nonrandom manner.

Circumstellar gas associated with HL Tauri - Evidence for a remnant infalling envelope

Molecular carbon absorption lines in the spectrum of HL Tau has been discovered near 8775 A. These C2 lines have a heliocentric radial velocity of 43 + or - 3 km/s, redshifted by 23 + or - 3 km/s relative to the star and the associated molecular cloud. This velocity difference suggests that the molecular carbon absorption arises in an infalling envelope. Since KI and diffuse interstellar bands are much weaker than expected, the chemical composition and/or excitation conditions in the HL Tau envelope appear to differ substantially from those in the interstellar medium. 19 refs.

Lithium line variations in weak-lined T Tauri stars

We have observed seven weak-lined T Tauri stars to examine the effects of magnetic activity on the Li I 6707 A equivalent width and line profile. Six of the seven program stars were observed at least twice per evening on four consecutive nights. Variable Li I equivalent width is certainly present in two targets, which are the only known binaries (single-lined spectroscopic) in our sample, and likely in three others. The amplitude of the variability is consistent with previous estimates of activity effects. The variability itself supports hypotheses that observed spread in Li I equivalent widths may be explained by magnetic activity. It is unclear whether or not the binary nature of our two detections is significant. We find no indication that similarity to RS CVn systems, other than rapid rotation, is responsible for the variable activity detected

Rosat observations of FK comae berenices

We obtained ROSAT PSPC observations of FK Com over a period of 24.4 h, or 0.42 rotation. During the observations the x-ray flux increased by a factor of at least 5 before declining toward its previous level. A single temperature Raymond-Smith model is adequate to model the low signal-to-noise ratio spectrum from each observation interval. Initially the spectrum was that of a 8.5 x 10(exp 6) K plasma, with L9sub x)=0.66 x 10(exp 31) erg s(exp -1). When the x-ray flux was greatest, the model plasma temperature rose to 2.5 x 10(exp 7) K, and L(sub x)=3.46 x 10(exp 31) ergs(exp -1). During the post-maximum decline in luminosity the plasma temperature was approximately 12 x 10(exp 6) K. We conclude that the increase of x-ray flux recorded by ROSAT was due to an x-ray flare with a 1.5 h decline time scale.

Further evidence for differential rotation in V1057 Cygni

Further tests of the accretion disk hypothesis for FU Orionis objects are presented. High spectral resolution, high signal to noise, 5820-6830 A and 7500-9370 A spectra of V1057 Cyg reveal a correlation between linewidth and line transition lower excitation potential expected from this hypothesis. The magnitude of the effect compares favorably with that predicted by synthetic disk spectra. Additional evidence for previously documented spectral type and linewidth versus wavelength correlations is also presented. This kinematic evidence strongly supports the accretion disk hypothesis. 16 refs.