High-dispersion Optical Spectra Research Articles

A CORRELATION BETWEEN CIRCUMSTELLAR DISKS AND ROTATION IN THE UPPER SCORPIUS OB ASSOCIATION

We present projected rotational velocities for 20 early-type (B8-A9) and 74 late-type (F2-M8) members of the ~5 Myr old Upper Scorpius OB Association derived from high dispersion optical spectra obtained with the High Resolution Echelle Spectrometer (HIRES) on Keck I and the Magellan Inamori Kyocera Echelle (MIKE) on the Magellan Clay telescope. The spectroscopic sample is composed of stars and brown dwarfs with infrared signatures of circumstellar disks, both primordial and debris, and non-excess sources of comparable spectral type. We merge projected rotational velocities, accretion diagnostics, and Spitzer Space Telescope Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) 24 micron photometry to examine the relationship between rotation and circumstellar disks. The rotational velocities are strongly correlated with spectral type, a proxy for mass, such that the median vsini for B8-A9 type stars is: 195(+/-)70 km/s, F2-K4: 37.8(+/-)7.4 km/s, K5-K9: 13.8(+21.3/-8.2) km/s, M0-M5: 16.52(+/-)5.3 km/s, and M5.5-M8: 17.72(+/-)8.1 km/s. We find with a probability of >0.99 that M-type stars and brown dwarfs having infrared excess suggestive of circumstellar disks rotate more slowly than their non-excess counterparts. A similar correlation is present among F2-K9 type stars, but only at the ~97% confidence level. Among the early-type (B8-A9) members, rotational velocities of the debris-disk and non-disk populations are indistinguishable. Considering the late-type (F2-M8) stars and brown dwarfs, we find a low fraction of slowly rotating, non-excess sources relative to younger star forming regions, suggesting that most have spun up following disk dissipation. The few late-type (F2-M5) debris disk sources, which may be representative of stars that have recently dispersed their inner disks, are evenly divided between slow and moderate rotators.

The Low-Mass Companion to the Lithium-Depleted, Spectroscopic Binary HBC 425 (St 34)

ABSTRACTWe present high angular resolution, near-infrared imaging, and spectroscopy of a low-mass companion to the lithium-depleted, double-line spectroscopic binary HBC 425 (St 34) obtained using NIRSPEC and the Keck II adaptive optics system. Positioned ∼1.23″ southeast of the primary pair, the companion, HBC 425C, is ∼2.4 mag fainter at 2.2 μm. Moderate-resolution (R ∼ 2500) J- and K-band spectroscopy reveals HBC 425C to have an M5.5 (± 0.5) spectral type. Comparisons with pre–main-sequence evolutionary models imply a mass of ∼0.09 M⊙ and ages of 8–10 Myr, assuming the nominal distance of Taurus-Auriga (∼140 pc), or ∼25 Myr if placed at ∼90 pc. We also present high-dispersion optical spectra of HBC 425 and HBC 425C obtained using the high-resolution echelle spectrometer (HIRES) on Keck I. We detect strong Li i λ6708 absorption in the spectrum of HBC 425C. Using curves of growth for the Li i λ6708 doublet, we estimate its abundance level to lie between log N(Li) = 1.9 and 3.1 dex. The spectrum of HBC 425 exhibits Ca ii H and K lines, He i λλ5876, 6678, and strong Balmer line emission, consistent with accretion. We place more restrictive upper limits on the surface abundance of lithium and find that HBC 425 retains less than ∼0.1% of its primordial abundance. The presence of lithium in the photosphere of HBC 425C does not resolve the discrepancy between isochronal and lithium-depletion ages for the primary pair. However, if lithium were depleted relative to interstellar abundance levels, even minimally, considerable support would be gained for the more advanced age of this hierarchical triple system.

A DETAILED LOOK AT CHEMICAL ABUNDANCES IN MAGELLANIC CLOUD PLANETARY NEBULAE. I. THE SMALL MAGELLANIC CLOUD

We present an analysis of elemental abundances of He, N, O, Ne, S, and Ar in Magellanic Cloud planetary nebulae (PNe), and focus initially on 14 PNe in the Small Magellanic Cloud (SMC). We derived the abundances from a combination of deep, high dispersion optical spectra, as well as mid-infrared (IR) spectra from the Spitzer Space Telescope. A detailed comparison with prior SMC PN studies shows that significant variations among authors of relative emission line flux determinations lead to systematic discrepancies in derived elemental abundances between studies that are >~0.15 dex, in spite of similar analysis methods. We used ionic abundances derived from IR emission lines, including those from ionization stages not observable in the optical, to examine the accuracy of some commonly used recipes for ionization correction factors (ICFs). These ICFs, which were developed for ions observed in the optical and ultraviolet, relate ionic abundances to total elemental abundances. We find that most of these ICFs work very well even in the limit of substantially sub-Solar metallicities, except for PNe with very high ionization. Our abundance analysis shows enhancements of He and N that are predicted from prior dredge-up processes of the progenitors on the AGB, as well as the well known correlations among O, Ne, S, and Ar that are little affected by nucleosynthesis in this mass range. We identified MG_8 as an interesting limiting case of a PN central star with a ~3.5 M_sun progenitor in which hot-bottom burning did not occur in its prior AGB evolution. We find no evidence for O depletion in the progenitor AGB stars via the O-N cycle, which is consistent with predictions for lower-mass stars. We also find low S/O ratios relative to SMC H_II regions, with a deficit comparable to what has been found for Galactic PNe.

Dynamical Evidence for a Massive, Young Globular Cluster in NGC 1569

Recent high-resolution observations with the Hubble Space Telescope (HST) reveal that star of extraordinary luminosity and compactness are commonly found in a variety of starburst systems. There has been much speculation that these represent present-day analogs of young globular clusters. Using the HIRES echelle spectrograph on the Keck 10 m telescope, we obtained high-dispersion optical spectra of one of the super star clusters (cluster A) in the nearby dwarf galaxy NGC 1569. The size of the cluster is known from published HST images. The line-of-sight velocity dispersion (σ* = 15.7 ± 1.5 km s-1) has been measured from a cross-correlation analysis of its integrated spectrum at visual wavelengths. If the cluster is gravitationally bound and the velocities are isotropic, application of the virial theorem implies that the cluster has a total stellar mass of (3.3 ± 0.5) × 105 M☉. This object's mass, mass density, and probable mass-to-light ratio after aging 10-15 Gyr are fully consistent with the typical values of Galactic globular clusters. Our result strongly suggests that at least some of the luminous, compact, young star being discovered with HST will indeed evolve into normal globular of the type seen in the Milky Way.

Model Atmosphere and Kinematical Analyses of Early-Type, High Galactic Latitude Stellar Candidates from the UKST UBVRI Survey

view Abstract Citations (14) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Model Atmosphere and Kinematical Analyses of Early-Type, High Galactic Latitude Stellar Candidates from the UKST UBVRI Survey Hambly, N. C. ; Conlon, E. S. ; Dufton, P. L. ; Keenan, F. P. ; Little, J. E. ; Miller, L. Abstract From the UKST UBVRI survey, six high Galactic latitude stars have been previously identified which may be young hydrogen-burning objects. Using high-dispersion optical spectra, model atmosphere analyses are presented for these targets. Two have normal or nearly normal Population I chemical compositions, one appears to be subluminous while the remaining three are possibly normal late B-type stars. A kinematic analysis indicates that one star having normal parameters is an excellent candidate for formation in the halo, having an evolutionary age an order of magnitude less than the time required for it to attain its current position following ejection from the Galactic disk. A preliminary analysis implies that there may currently be a few thousand normal B-type stars in the Galactic halo with z-distances from the plane of the Galaxy in the range 3 < Ζ < 22 kpc. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173349 Bibcode: 1993ApJ...417..706H Keywords: STARS: ABUNDANCES; STARS: ATMOSPHERES; STARS: EARLY-TYPE; STARS: EVOLUTION full text sources ADS | data products SIMBAD (5) Related Materials (2) Source Software: 2014ascl.soft06017W Used in: 1987MNRAS.225..761F

X-ray sources in regions of star formation. IV - High-resolution optical spectroscopy of X-ray identified candidate pre-main-sequence stars in the Chamaeleon I cloud

view Abstract Citations (35) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-Ray Sources in Regions of Star Formation. IV. High-Resolution Optical Spectroscopy of X-Ray Identified Candidate Pre-Main-Sequence Stars in the Chamaeleon I Cloud Walter, Frederick M. Abstract I present and discuss high dispersion optical spectra of 11 of the optical counterparts of the x-ray sources associated with the Cha I dark cloud. Feigelson & Kriss [ApJ, 338, 262 (1989)] suggested that eight of these were likely naked T Tauri stars, based on low dispersion optical spectra. We concur with four of the classifications; of the others, one star is a BY Dra binary, one is a classical T Tauri star and two are foreground or background stars. We also identify two naked T Tauri stars among stars Feigelson and Kriss did not observe. Publication: The Astronomical Journal Pub Date: August 1992 DOI: 10.1086/116271 Bibcode: 1992AJ....104..758W Keywords: Astronomical Spectroscopy; Molecular Clouds; Star Formation; T Tauri Stars; X Ray Sources; Binary Stars; Dark Matter; H Alpha Line; Radial Velocity; Stellar Spectra; Astrophysics; STARS: PRE-MAIN SEQUENCE full text sources ADS | data products SIMBAD (17) Related Materials (5) Part 1: 1986ApJ...306..573W Part 2: 1987ApJ...314..297W Part 3: 1988AJ.....96..297W Part 5: 1994AJ....107..692W Part 6: 1997AJ....114.1544W

Radial velocities of stars with microwave maser emission. I Long-period variables

view Abstract Citations (53) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radial velocities of stars with microwave maser emission. I. Long-period variables. Wallerstein, G. Abstract Extensive radial-velocity measurements of high-dispersion optical spectra (wavelengths within 3500-9000 A) of long-period variables are presented and analyzed so as to establish the photospheric, emission, and circumstellar velocities. The data are compared with microwave emission velocities from the molecules OH, H2O, and SiO. Correlations among the various velocities are presented and discussed. At least one microwave component has the same velocity as the stellar photosphere, and frequently one or more microwave velocities agree with the velocity of the circumstellar envelope. Other microwave components frequently fall between the photospheric and circumstellar velocities. The question of whether the absorption or emission lines represent the true stellar velocity is discussed. The correlations among the microwave and stellar absorption velocities favor the absorption velocity as representative of the center of mass. However, the possibility remains that the velocities of the permitted and forbidden lines represent the stellar velocity, provided that the emission lines are formed at small optical depth and hence are strongly limb-brightened. Publication: The Astrophysical Journal Supplement Series Pub Date: September 1975 DOI: 10.1086/190350 Bibcode: 1975ApJS...29..375W Keywords: Microwave Emission; Radial Velocity; Stellar Envelopes; Variable Stars; Astronomical Catalogs; Emission Spectra; Molecular Spectra; Photosphere; Velocity Distribution; Astrophysics full text sources ADS | data products SIMBAD (19)