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Stapelfeldt, Karl R.

Publications and source records attributed to Stapelfeldt, Karl R..

23 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

(abstract) The Absorption Line Spectra of Herbig-Hiro Object Exciting Stars at 1.6 and 2 Microns

We observed six Herbig-Hiro object exciting stars with the IRTF CSHELL cryogenic echelle spectrometer at 1.6 and 2 microns with the intent of determining effective temperatures and vsini's from the absorption lines in these spectral regions. In all of these objects, the photospheric absorption lines were either very weak or undetectable with our modest S/N high spectral resolution data. Using this information, constraints can be placed on the veiling continuum present at these wavelengths for embedded low-mass YSOs.

Herbig-Hiro object exciting stars spectrometry abs↗
NASA NTRS1994

W134: A new pre-main-sequence double-lined spectroscopic binary

We report the discovery that the pre-main-sequence star Walker 134 in the young cluster NGC 2264 is a double-lined spectroscopic binary. Both components are G stars with strong Li I 6708 A absorption lines. Twenty radial velocity measurements have been used to determined the orbital elements of this system. The orbit has a period of 6.3532 +/- 0.0012 days and is circular within the limits of our velocity resolution; e less than 0.01. The total system mass is stellar mass sin(exp 3) i = 3.16 solar mass with a mass ratio of 1.04. Estimates for the orbit inclination angle and stellar radii place the system near the threshold for eclipse observability; howerver, no decrease in brightness was seen during two attempts at photometric monitoring. The circular orbit of W 134 fills an important gap in the period distribution of pre-main-sequence binaries and thereby constrains the effectiveness of tidal orbital circularization during the pre-main sequence.

Padgett, Deborah L.↗
NASA NTRS1993

Circumstellar molecular gas of the HH 34 and HH 111 exciting stars

The HH 34 and HH 111 exciting stars, two pre-main-sequence objects which are the sources of highly collimated optical jets, have been observed in the J = 1-0 transition of (C-13)O and in the 2.7 mm continuum using the Owens Valley Radio Observatory Millimeter Interferometer. The high-resolution aperture synthesis maps reveal dense molecular gas concentrations at the positions of both stars. The morphology and kinematics of the bright emission-line cores suggest that the molecular gas is distributed in circumstellar disks, each about 2000 AU in diameter, elongated perpendicular to each system's outflow axis. A fainter component of (C-13)O emission extends along each source's outflow axis. Independent mass determinations based on the dust continuum and molecular line fluxes indicate for HH 34, a disk mass of 0.2 solar mass; and for HH 111, a disk mass of 0.3 solar mass. The inferred circumstellar disks of these two jet sources are significantly more massive than those found associated with T Tauri stars and are therefore among the most massive disks known in association with low-mass pre-main-sequence stars.

Stapelfeldt, Karl R.↗
NASA NTRS1991

Near-infrared emission-line images of three Herbig-Haro objects

Flux-calibrated imagery in five emission-line and four narrow-band continuum filters are presented for three classical Herbig-Haro (HH) objects, HH 7-11, HH 12, and HH 34. 1.64 micron forbidden Fe II emission is detected in all three objects whose intensity is typically 20 percent. This line should be an excellent tracer of shocked ionized gas in highly obscured regions. Extinction appears to be unimportant in determining the morphology of these HH object systems. No near-IR continuum emission was detected from any of the HH objects, implying that these regions do not contain embedded stars. At positions where the flow terminates against a large obstacle, there are significant offsets between the shocked flow material and the shocked ambient medium.

Stapelfeldt, Karl R.↗