Stellar Spectroscopy Research Articles

Infrared imaging and spectroscopy of NGC 7469

view Abstract Citations (171) References (98) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Imaging and Spectroscopy of NGC 7469 Genzel, R. ; Weitzel, L. ; Tacconi-Garman, L. E. ; Blietz, M. ; Cameron, M. ; Krabbe, A. ; Lutz, D. ; Sternberg, A. Abstract As part of an extensive study of the infrared properties of luminous galactic nuclei we report here subarcsecond-resolution near-infrared imaging and spectroscopy of the nucleus of the Seyfert 1 galaxy NGC 7469. Our measurements elucidate for the first time the spatial distribution of the near-infrared continuum and a number of bright near-infrared lines (Brγ, [Fe II], [Si VI], H_2_, He I, and CO) on a scale of less than a few hundred parsecs. We find that these tracers originate from three distinct components: the nucleus, a 1.5 (480 pc) radius circumnuclear ring/spiral-arm system with embedded knots, and a 1" ridge of blueshifted, radially streaming gas emanating southward from the nucleus. The circumnuclear ring is the location of a powerful starburst deeply embedded in a large concentration of molecular gas and dust and has a luminosity of ~3 x 10^11^ L_sun_, two-thirds of the bolometric luminosity of the entire galaxy. It contains a number of supergiant star formation regions with a few 10^4^ OB stars each. Our 0.4" resolution near-infrared images do not show evidence for a stellar bar. Gas influx into the nucleus and starburst ring were most likely triggered => 10^8^ yr ago by the interaction of NGC 7469 with its neighbor, IC 5283. A comparison of the mass derived from gas and stellar dynamics and from the CO 1-0 millimeter line emission suggests that the conversion factor from molecular hydrogen column density to integrated CO flux [X = N(H_2_)/I(CO)] in the central 800 pc is significantly smaller than in the Galactic disk, presumably as the result of the impact of the intense star formation activity on the surrounding interstellar medium. We have carried out a quantitative analysis of the ring's visible, infrared, and radio emission using star cluster models. The data are well fit by two types of solutions. One possibility is that the star formation rate has been constant (~30 M_sun_ yr^-1^) over the last several 10^7^ yr and stars more massive than 30-40 M_sun_ have not been forming during this period. An alternative model that does not require an upper mass cutoff is a decaying burst with a decay time significantly less than its present age (~1.5 x 10^7^ yr). For both star formation histories and for the small N(H_2_)/I(CO) conversion factor mentioned above, the star formation efficiency in NGC 7469 is high and the burst is soon going to end because the gas reservoir is exhausted. Our 2.1 micron H_2_ S(1) line maps show that there is a large concentration of molecular gas close to the Seyfert 1 nucleus of NGC 7469. The central 10^2^ pc of NGC 7469 contains 10^8+/-1 M_sun_ of neutral interstellar gas, consistent with current unifying models for Seyfert 1 and 2 nuclei. Broad (FWHM 1400 km s^-1^) 1.96 micron [Si VI] line emission arises in moderately dense (n_e_ >= 10^2^ cm^-3^) gas within a few 10^2^ pc from the nucleus. Our work clearly shows that NGC 7469 is a luminous Seyfert galaxy whose total energy output is predominantly powered by star formation. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175588 Bibcode: 1995ApJ...444..129G Keywords: Astronomical Spectroscopy; Galactic Nuclei; Infrared Astronomy; Infrared Imagery; Infrared Spectroscopy; Near Infrared Radiation; Seyfert Galaxies; Emission; Interacting Galaxies; Interstellar Matter; Molecular Gases; Spatial Distribution; Star Formation; Star Formation Rate; Starburst Galaxies; Astronomy; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 7469; GALAXIES: ISM; GALAXIES: NUCLEI; GALAXIES: SEYFERT; GALAXIES: STELLAR CONTENT; INFRARED: GALAXIES; STARS: FORMATION full text sources ADS | data products SIMBAD (12) NED (1)

Spectroscopy of candidate young globular clusters in NGC 1275

view Abstract Citations (43) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy of Candidate Young Globular Clusters in NGC 1275 Zepf, Stephen E. ; Carter, Dave ; Sharples, Ray M. ; Ashman, Keith Abstract We present spectra of the brightest member of the population of compact blue objects discovered in the peculiar galaxy NGC 1275 by Holtzman et al. (1992) using Hubble Space Telescope images. These spectra show strong Balmer absorption lines like those observed in A-type stars, as expected if the object is a young globular cluster. The age estimated from the strength of the Balmer lines is about 0.5 Gyr, although ages ranging from 0.1 Gyr to 0.9 Gyr cannot be confidently excluded given current models of stellar populations. If these estimated ages are adopted for the young cluster population of NGC 1275 as a whole, the fading predicted by stellar populations models gives a luminosity function which is consistent with that of the Galactic globular cluster system convolved with the observational selection function for the NGC 1275 system. We also use the equivalent widths of the Mg b and Fe 5270 features to constrain the metallicity of the young cluster. Combining these absorption-line widths with the age estimates from the Balmer lines and stellar population models, we find a metallicity of roughly solar, based on the Mg b index, and somewhat higher for the Fe 5270 index. The radial velocity of the absorption lines of the cluster spectrum is offset from the emission lines of the galaxy spectrum at the same position by -130 km s^-1^, providing further evidence for the identification of the object as a globular cluster and opening up the future possibility of studying the kinematics of young cluster systems. The discovery of objects with the characteristics of young globular clusters in NGC 1275, which shows evidence of a recent interaction or merger, supports the hypothesis that galaxy interactions and mergers are favorable sites for the formation of globular clusters. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/187879 arXiv: arXiv:astro-ph/9503050 Bibcode: 1995ApJ...445L..19Z Keywords: Absorption Spectra; Astronomical Spectroscopy; Balmer Series; Galactic Clusters; Galactic Radiation; Globular Clusters; Blue Stars; Galactic Evolution; Hubble Space Telescope; Interacting Galaxies; Luminosity; Stellar Models; Space Radiation; GALAXIES: FORMATION; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1275; GALAXIES: INTERACTIONS; GALAXIES: STAR CLUSTERS; Astrophysics E-Print: 12 pages uuencoded, compressed postscript, accepted for publication in the Astrophysical Journal Letters full text sources arXiv | ADS | data products SIMBAD (5) NED (1) MAST (1) ESA (1)

GHRS observations of cool, low-gravity star. 2: Flow and turbulent velocities in the outer atmosphere of gamma CRU CIS (M3.4 III)

view Abstract Citations (28) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS GHRS Observations of Cool, Low-Gravity Stars. II. Flow and Turbulent Velocities in the Outer Atmosphere of gamma Crucis (M3.4 III) Carpenter, Kenneth G. ; Robinson, Richard D. ; Judge, Philip G. Abstract The Goddard High Resoulution Spectrograph (GHRS) on the Hubble Space Telescope (HST) has been used to obtain medium (R = 20,000) and high (R = 85,000) resoultion UV spectra of chromosphere emission features for the M3.4 III star gamma Cru. Small Science Aperture (SSA) G270M and Echelle-B spectra of selected regions in the 2300-2850 A range were obtained to determine the kinematics of the chromosphere using lines of C2), Fe2, Co2, Si1/2), Ni2, Mn2, and Mg2. Profiles of C2) (UV 0.01) lines and fluorescently excited lines of low optical depth indicate average turbulent velocities (Doppler FWHM) of 30.2 +/- 1.3 and 28.8 +/- 1.3 km/s, respectively. The fluorescent emission lines (mean RV = 21.3 +/- 0.9 km/s) and the wings of the emission components of Fe2 lines (mean RV = 22.8 +/- 0.4 km/s) are approximately at rest relative to the radial velocity of the star (21 km/s), while the C2) lines show a modest inflow (mean RV = 23.1 +/- 0.9 km/s). The more opaque lines of Fe2 and Mg2 exhibit complex profiles resulting from line formation in an optically thick, extended expanding atmosphere. The emission wings of these lines are broadened by multiple scattering, and they are centered near the photospheric radial velocity. Closer to line center, these strong lines show a strong blueshifted self-absorption feature (already seen in IUE data), indicative of formation in an expanding chromosphere, and a previously unseen dip in the profiles on the red side of line center. The absorption components, when extracted using simple Gaussian fits, show strong correlations with the relative optical depths of the lines. The derived absorption flow velocities converge to the photospheric velocity as one examines spectra features formed deeper in the atmosphere. The blueward abosrption velocity increases in magnitude from about 7 to 14 km/s with increasing line optical depth - the strong absorptions directly map the acceleration of the outflowing stellar wind, while the interpretation of the weaker redshifted absorptions is more ambiguous, indicating either an inflow of material or formation in an extended, spherically expanding outflow. The Mg2 and Fe2 profiles, taken together, imply that the wind speed decreases between the atmospheric layers where the Mg2 and Fe2 self-absorption components are formed. Interstellar absorptions are seen in the resonance lines of Mg2 (UV 1) and Fe2 (UV1) with zero-volt lower levels, at about -3 km/s, consistent with models of the interstellar medium in the direction of gamma Cru. Finally, we have detected the Mg2 'satellite lines' seen in solar spectra obtained above the limb. In gamma Cru these lines are probably fluorescently excited by H Ly beta. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175617 Bibcode: 1995ApJ...444..424C Keywords: Astronomical Spectroscopy; Cool Stars; Flow Velocity; Stellar Atmospheres; Stellar Spectra; Turbulence; Ultraviolet Astronomy; Absorption Spectra; Chromosphere; Emission Spectra; Hubble Space Telescope; Stellar Winds; Ultraviolet Spectra; Astronomy; STARS: CHROMOSPHERES; STARS: INDIVIDUAL CONSTELLATION NAME: GAMMA CRUCIS; STARS: LATE-TYPE; TURBULENCE; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (3) MAST (2) ESA (1) Related Materials (4) Part 1: 1994ApJ...428..329C Part 3: 1997ApJ...479..970C Part 4: 1998ApJ...503..396R Part 5: 1999ApJ...521..382C

Detection of a series of methanol maser lines at 1.9 millimeter wavelength

view Abstract Citations (36) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of a Series of Methanol Maser Lines at 1.9 Millimeter Wavelength Slysh, V. I. ; Kalenskii, S. V. ; Val'tts, I. E. Abstract The series of methanol J0-J-1 E lines at 157 GHz has been detected in known methanol line sources together with the 21-30 A+ line of A-type methanol. In W3(OH), 345.01+1.79, W48, and Cep A the Jo-J-1 lines are intense and narrow and are believed to be maser lines. The radial velocities and profiles are similar to those of other class II methanol lines in these sources. The intensity of the lines increases with rotational number J, in contrast to thermal methanol features which were detected in the same sources at slightly different radial velocities. It is suggested that the new maser line sources are the class II methanol masers but are excited with higher radiation temperature than the lower frequency class II masers at 6.7 and 12.2 GHz. The masers may be related to molecular outflows or cometary bow shocks of ultracompact H II regions as is evidenced by their velocity shift relative to the parent molecular clouds. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175471 Bibcode: 1995ApJ...442..668S Keywords: H Ii Regions; Interstellar Masers; Line Spectra; Methyl Alcohol; Millimeter Waves; Molecular Clouds; Radio Astronomy; Velocity Distribution; Astronomical Spectroscopy; Molecular Flow; Molecular Rotation; Shock Waves; Spectrum Analysis; Thermal Emission; Astronomy; ISM: H II REGIONS; ISM: MOLECULES; MASERS; MOLECULAR PROCESSES full text sources ADS | data products SIMBAD (5)

On the nature of spectral features in peculiar DQ white dwarfs

view Abstract Citations (60) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Nature of the Spectral Features in Peculiar ``DQ'' White Dwarfs Schmidt, Gary D. ; Bergeron, P. ; Fegley, Bruce Abstract Spectropolarimetric measurements are presented for the DQ white dwarfs ESO 439-162, LHS 1126, and G225-68, whose spectroscopic features in the optical have been interpreted in the past as pressure-shifted or magnetically shifted C2 Swan bands. The results convincingly demonstrate that none of these objects is strongly magnetic, with upper limits of 30, 3, and 2 MG respectively. Since Bergeron et al. (B 94) have recently ruled out the pressure-shift interpretation for LHS 1126 as well, we discuss alternative physical mechanisms for displacing the Swan bands. Although possibilities for explaining the observed shifts may exist, a comparison of the optical spectra (and that of a similar DQ star, LP 77-57) indicates that the locations and shapes of the profiles in all four objects are virtually identical. This last result suggests instead that a different molecular species could be responsible. A detailed chemical equilibrium analysis of H/He/C mixtures under the physical conditions encountered in the atmospheres of these peculiar objects reveals that C2H is a molecule preferentially formed in the photospheric regions. The nature and evolution of these objects are discussed. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175524 Bibcode: 1995ApJ...443..274S Keywords: Polarization; Spectrum Analysis; Swan Bands; White Dwarf Stars; Abundance; Astronomical Polarimetry; Astronomical Spectroscopy; Carbon Compounds; Frequency Shift; Helium; Hydrogen; Stellar Magnetic Fields; Visible Spectrum; Astrophysics; POLARIZATION; STARS: ABUNDANCES; STARS: ATMOSPHERES; STARS: MAGNETIC FIELDS; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (9)

Infrared line emission from high-redshift galaxies. 1: Calculations

view Abstract Citations (18) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Line Emission from High-Redshift Galaxies. I. Calculations Mannucci, Filippo ; Beckwith, Steven V. W. Abstract The first generation of stars at high redshift should have produced bright optical lines of common elements. These lines would appear now in near-infrared bands. We estimate the line fluxes and large-area surface brightnesses of the prominent lines Lyα, Hα, Hβ, [O III] λ5007, and [O II] λ3727 from the first galaxies under a variety of assumptions about the epochs of star formation and cosmology. The results show that these galaxies are within the reach of the present generation of infrared instrumentation for a wide range of star formation histories. We discuss the efficacy of searching for emission-line objects in the near-infrared as a means of finding primeval galaxies and discuss the possible searching strategies with respect to the expected intrinsic scatter of the properties of the forming galaxies. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175460 Bibcode: 1995ApJ...442..569M Keywords: Emission Spectra; Galactic Evolution; Infrared Astronomy; Infrared Spectra; Line Spectra; Star Formation; Stellar Composition; Astronomical Spectroscopy; Cosmic Dust; Near Infrared Radiation; Star Distribution; Stellar Luminosity; Astrophysics; GALAXIES: EVOLUTION; GALAXIES: STELLAR CONTENT; INFRARED: GALAXIES; LINE: FORMATION full text sources ADS | data products SIMBAD (1)

Discovery of a transient MeV range gamma-ray source

view Abstract Citations (14) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a Transient MeV Range Gamma-Ray Source Briggs, M. S. ; Gruber, D. E. ; Matteson, J. L. ; Peterson, L. E. Abstract The University of California, San Diego (UCSD)/MIT hard X-ray and gamma-ray instrument on the HEAO 1 surveyed the region near the Galactic center 3 times during its lifetime in 1977-1979. During the 1977 September-October scan, a gamma-ray source was detected south of the Galactic center. The source was below the threshold sensitivity in the spring and fall of 1978. The source was detected with the medium energy phoswich scintillation counters which operated over the 80 keV-2 MeV range, had an area of 42 sq cm each, and a 17 deg FWHM aperture. The error box for the source is centered on l = 2.4 deg, b = -12.2 deg, with a 90% confidence error circle of approximately 3.5 deg radius. The flux in the 333-635 keV range was (1.89 +/- 0.29) x 10-5 photons/(sq cm s keV) and was constant within statistics during the 1 month period the source was in the field of view. The spectrum can be characterized as a Gaussian in the range 300 less than or = E less than or = 650 keV, with a FWHM of 249 +/- 51 keV centered on 461 +/- 22 keV. The flux of this broad Gaussian is (6.6 +/- 1.1) x 10-3 photons/(sq cm s). The source is tentatively identified with the 5.57 hr period low-mass X-ray-emitting binary system 1H 1822-371. Assuming this is correct, the ratio of gamma-ray to X-ray luminosity during the outburst was about 5; at a distance of 8 kpc, the gamma ray luminosity is 4 x 1037 ergs. The emission may be interpreted as a positron-pair plasma ejected from a compact object, possibly a black hole, and annihilating in a thick accretion disk surrounding the object. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175467 Bibcode: 1995ApJ...442..638B Keywords: Accretion Disks; Black Holes (Astronomy); Galactic Nuclei; Gamma Ray Astronomy; Gamma Ray Bursts; Gamma Ray Spectra; Milky Way Galaxy; X Ray Astronomy; X Ray Binaries; Astrometry; Astronomical Spectroscopy; Data Reduction; Flux Density; Heao 1; Spaceborne Astronomy; Stellar Luminosity; Astronomy; GALAXY: CENTER; GAMMA RAYS: BURSTS; STARS: BINARIES: CLOSE; X-RAYS: STARS full text sources ADS | data products SIMBAD (15)

Effects of prescattering attenuation of spectropolarimetric line profiles

view Abstract Citations (11) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effects of Prescattering Attenuation on Spectropolarimetric Line Profiles Wood, Kenneth ; Bjorkman, J. E. Abstract We present the wavelength dependent linear polarization and position angle variations arising from single Thomson scattering of continuum stellar radiation in an axisymmetric, hot, planar disk, which is in bulk motion. The wavelength dependence arises through the combination of Doppler shifted line attenuation, prior to scattering, and the Doppler redistribution of the scattered radiation due to the bulk and thermal motions of the disk electrons. We find that when the scattering electrons are cold, there are large polarization and position angle variations across the resulting spectrapolarimetric absorption line profile-agreeing with previous investigations. However, when the thermal Doppler velocities of the scattering electrons are comparable to or greater than the electron bulk velocity (as is of ten the case), then the scattered line profile is broadened and the amplitude of the polarimetric variations are considerably reduced. The properties of the electron thermal smearing function are such that the equivalent width of any scattered spectrapolarimetric feature is independent on the electron temperature-a consequence of the conservation of areas under convolution. An important result of this is that for an axisymmetric circumstellar envelope the position angle variations will average to zero across any line formed through the above process. We expect that the effect of multiple line blending will yield a depolarization equivalent width is given by the sum of the individual equivalent widths and the position angle variations will average to zero. The implications of this are that the large depolarizations observed in the UV spectra of pi Aquarii, zeta Tauri and PP Carinae by the Wisconsin Ultraviolet Photo Polarimeter Experiment (WUPPE) can only be explained with prescattering attenuation of stellar flux if there are a sufficient number of multiple overlapping lines in that part of the spectrum. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175530 Bibcode: 1995ApJ...443..348W Keywords: Attenuation; Line Spectra; Linear Polarization; Planar Structures; Position (Location); Stellar Radiation; Thomson Scattering; Wavelengths; Astronomical Polarimetry; Astronomical Spectroscopy; Doppler Radar; Electron Energy; Spectrographs; Stellar Envelopes; Ultraviolet Spectra; Astrophysics; INSTRUMENTATION: SPECTROGRAPHS; LINE: PROFILES; POLARIZATION; STARS: CIRCUMSTELLAR MATTER; STARS: EMISSION-LINE; BE full text sources ADS | data products SIMBAD (4) MAST (1)

Interstellar titanium in the galactic halo

view Abstract Citations (20) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar Titanium in the Galactic Halo Lipman, Keith ; Pettini, Max Abstract We present observations of Ti~II~$\lambda 3384$ absorption towards 15 distant stars in the Galactic halo and the Magellanic Clouds. These new data extend existing surveys of the distribution of Ti$^+$ to larger distances from the plane of the Galaxy than sampled previously, allowing the scale height of titanium to be determined for the first time. We find $h_{Ti^+} = 1.5 \pm 0.2$~kpc, a value which although greater than those of other tracers of neutral gas, is not as large as had been suspected. We interpret the extended distribution of Ti$^+$ as an indication that its severe depletion in interstellar clouds in the disk is reduced at the lower densities prevailing in the halo. The data are consistent with a simple power-law dependence of the Ti abundance on the ambient density, with exponent $k \simeq -1$. If the model is correct, it implies that refractory elements like Ti are fully returned to the gas phase at distances beyond $\sim 1$ kpc from the plane of the Galaxy. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175466 arXiv: arXiv:astro-ph/9410074 Bibcode: 1995ApJ...442..628L Keywords: Absorption Spectra; Galactic Halos; Interstellar Gas; Magellanic Clouds; Milky Way Galaxy; Titanium; Ultraviolet Astronomy; Ultraviolet Spectra; Abundance; Astronomical Spectroscopy; Density (Number/Volume); Scale Height; Spectrum Analysis; Astronomy; GALAXIES: MAGELLANIC CLOUDS; GALAXY: HALO; ISM: ABUNDANCES; Astrophysics E-Print: Accepted for publication in ApJ, due to appear 1 April 1995. 23 pages including 5 figures full text sources arXiv | ADS | data products SIMBAD (17)

Color-magnitude diagrams for clusters 2 and 4, and the field in the Fornax dwarf spheroidal galaxy

view Abstract Citations (37) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Color-Magnitude Diagrams for Clusters 2 and 4, and the Field in the Fornax Dwarf Spheroidal Galaxy Beauchamp, Dominique ; Hardy, Eduardo ; Suntzeff, Nicolas B. ; Zinn, Robert Abstract We present new results on the cluster system and the field of Fornax based on imaging and spectroscopic observations conducted at CTIO and CFHT. The color-magnitude diagram of Cluster 2 (C2), which reaches well below the horizontal branch confirms that it is a "bona fide" old globular cluster similar to the metal-poor globulars of the galaxy with well-developed blue horizontal branches. From the magnitude of its HB, V = 21.4 +/- 0.2, and assuming E(B- V) = 0.03+/-0.03, and M_v_(HB)= +0.6+/-0.2 we derive a corrected distance modulus of (V- M_v_)_0_ = 20.7+/-0.3 corresponding to a distance of 138_-18_^+20^ kpc. We have partially resolved Cluster 4 (C4) using HRCam at the CFH telescope and found its HB at V = 21.3 in excellent agreement with the results for C2. The giant branch of C4, which in our diagram consists of a small number of stars, indicates a low metallicity comparable to that of C2. However, integrated-light spectroscopy of the near IR Ca II triplet confirms the higher value of the metallicity found by other workers also from the study of the integrated light. The measurements of reliable parameters from the CMD of this very compact and highly contaminated cluster requires resolution closer to its center than we have been able to obtain. Our V, B, and I CMDs of the field of Fornax reach well below the level of the HB. They reveal a young main sequence, indicating that star formation has continued until about 2 Gyr ago. There is little evidence for the presence of a blue HB, and the giant branch contains a well-developed clump similar to those observed in intermediate-age populations in the_Magellanic Clouds, but of much lower mean metallicity. The metallicity of the field is well represented by [Fe/H]^bar^ = - 1.34 +/- 0.40 (full range). These abundance values are in good agreement with the results of previous investigations. The metallicity spread of 0.8 dex found in the field is similar to that found in the cluster system since [Fe/H]_cluster4_-[Fe/H]_cluster3_ = 0.7. Our CMD of C4 suggests that it is an old cluster not grossly different in age from the more metal-poor Fornax clusters. This in turn suggests that the metal enrichment of Fornax was rapid in comparison to its long history of star formation. Publication: The Astronomical Journal Pub Date: April 1995 DOI: 10.1086/117390 Bibcode: 1995AJ....109.1628B Keywords: Color-Magnitude Diagram; Dwarf Galaxies; Galactic Clusters; Globular Clusters; Abundance; Astronomical Spectroscopy; Asymptotic Giant Branch Stars; Magellanic Clouds; Main Sequence Stars; Metallicity; Space Observations (From Earth); Star Formation; Astronomy; GALAXIES: PECULIAR; GALAXIES: CLUSTERS: INDIVIDUAL: C2; GALAXIES: CLUSTERS: INDIVIDUAL: C4; GALAXIES: ABUNDANCES full text sources ADS | data products SIMBAD (55) NED (3)

Kinematics of the old open cluster system

view Abstract Citations (61) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematics of the Old Open Cluster System Scott, Jennifer E. ; Friel, Eileen D. ; Janes, Kenneth A. Abstract Radial velocities accurate to 15 km/s or better were determined for 11 open clusters older than approximately 1 GYR and distributed over a range of positions in the galaxy. Moderate resolution spectra of an average of 30 stars in each cluster of varying spectral types were obtained using the 4.0 m telescope at Kitt Peak National Observatory (KPNO) and the Hydra multi-object spectrograph. The radial velocities were calculated for the late type giants in each cluster using cross correlation techniques; and mean velocity values were obtained for five clusters with no previous radial velocity measurements: Be 17, Be 31, Be 32, King 5, and King 11. Using these data, along with published velocities for an additional 24 clusters, the mean difference between the velocities of the open clusters and those predicted by a standared rotation curve is 1 +/- 29 km/s. Also, assuming that the old open cluster system rotates about the Galactic center with a constant rotation velocity, this velocity is found to be 21 +/- 7 km/s with a line-of-sight dispersion of 28 km/s. Both of these results imply that the old open clusters are predominantly a thin disk population. Be 17, the oldest cluster in this sample, also exhibits peculiar kinematics, and is discussed in particular. Publication: The Astronomical Journal Pub Date: April 1995 DOI: 10.1086/117398 Bibcode: 1995AJ....109.1706S Keywords: Disk Galaxies; Galactic Rotation; Giant Stars; Kinematics; Late Stars; Milky Way Galaxy; Open Clusters; Radial Velocity; Astronomical Observatories; Astronomical Spectroscopy; Cross Correlation; Spectrographs; Astrophysics; OPEN CLUSTERS AND ASSCOIATIONS: GENERAL; GALAXY: KINEMATICS AND DYNAMICS full text sources ADS | data products SIMBAD (170)

Nonlinear spectroscopy in astronomy: assignement of diffuse interstellar absorption bands to L(α) -induced, two-photon absorption by H 2 molecules

All (twelve) optical diffuse interstellar absorption bands appearing in the interval 768.0–788.0 nm are assigned on the basis of a nonlinear effect: Lyman-alpha-driven, resonantly enhanced two-photon absorption by hydrogen molecules located near H II regions of young, hot stars.

Hydrogen chloride in OMC-1

view Abstract Citations (47) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrogen Chloride in OMC-1 Schilke, Peter ; Phillips, T. G. ; Wang, Ning Abstract We present a map of Orion Molecular Cloud (OMC-1) in the HCl (1-0) transition, observed with the Caltech Submillimeter Observatory (CSO). The line was detected toward almost all observed positions. It shows two distinct features, a ubiquitous narrow component, associated with the quiescent dense ridge and a broad component in the vicinity of IRc2, but associated with the outflow or plateau rather than with the hot core. An excitation analysis showed that the HCl line traces very dense (greater than 107/cc) gas. The fractional HCl abundance is constant within the errors (a few x 10-10 and shows neither variation with position nor between the two components. As a result, HCl is found not to be a significant coolant of the gas. The nondetection of a hot core component may be due to a low contrast between HCl excitation temperature and effective dust temperature and probably not to a low abundance in the hot core. The chemistry of HCl was reinvestigated, and it was found that HCl contains about one-third of the available gas phase chlorine, under the conditions in OMC-1. An upper limit to the chlorine depletion of 230 +/- 80 was determined. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175358 Bibcode: 1995ApJ...441..334S Keywords: Astronomical Models; Emission Spectra; Hydrogen Chlorides; Line Spectra; Molecular Clouds; Orion Nebula; Astronomical Spectroscopy; Chemical Analysis; Chlorine; Gas Temperature; Interstellar Matter; Astrophysics; ISM: ABUNDANCES; ISM: INDIVIDUAL ALPHANUMERIC: OMC-1; ISM: MOLECULES; MOLECULAR PROCESSES full text sources ADS | data products SIMBAD (1)

Imaging spectropolarimetry of the He I 1083 nanometer line in a flaring solar active region

view Abstract Citations (63) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Imaging Spectropolarimetry of the He i 1083 Nanometer Line in a Flaring Solar Active Region Penn, M. J. ; Kuhn, J. R. Abstract Slit spectra, simultaneously measuring left and right circular polarization of the solar spectrum at 1082.9 +/- 0.4 nm, were taken using the National Solar Observatory (NSO) Vacuum Tower Telescope (VTT) at Sacramento Peak with a 128 x 128 pixel HgCdTe IR camera. By moving the slit the solar active region NOAA 7629 was scanned with a cadence of 246 s from 1724 to 1902 UT on 1993 December 6. The region was in the decay phase of a C9.7 flare. Intensity, velocity and longitudinal magnetic field in both the Si I (photospheric) and He I (chromospheric) lines are computed from fits to the line profiles in left and right polarizations. Analysis of these quantities show: (1) He I line emission in three decaying flare kernels, (2) Zeeman splitting of the He I emission measuring the longitudinal magnetic field inside the flare kernels; (3) dark He I active region filaments avoid strong longitudinal chromospheric magnetic field, and an active filament (with a transverse speed of 9 km/s) produces fluctuations in the strength of the longitudinal magnetic fields, and (4) bipolar moving magnetic features (MMFs) and emerging active region bipoles (EARBs) are observed at photospheric but not chromospheric heights. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/187787 Bibcode: 1995ApJ...441L..51P Keywords: Chromosphere; Circular Polarization; Coronal Holes; Helium; Infrared Astronomy; Line Spectra; Linear Polarization; Photosphere; Solar Flares; Solar Magnetic Field; Astronomical Spectroscopy; Cameras; Charge Coupled Devices; Field Of View; Infrared Photography; Magnetic Signatures; Red Shift; Spectroheliographs; Spectroscopic Telescopes; Solar Physics; SUN: FLARES; SUN: INFRARED; SUN: MAGNETIC FIELDS full text sources ADS |

The brown dwarf candidate ESO 207-61: Its distance and very low luminosity

view Abstract Citations (7) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Brown Dwarf Candidate ESO 207-61: Its Distance and Very Low Luminosity Ianna, P. A. ; Fredrick, L. W. Abstract The relative trigonometric parallax we have measured for ESO 207-61 confirms its predicted very low luminosity. From southern CCD observations we find pirel = 0.0504 sec +/- 0.0026 sec giving absolute magnitudes of MV = 19.50 +/- 0.15, MK = 10.72 +/- 0.12, and Mbol = 13.88 +/- 0.27. It is one of the faintest objects found to date and has a spectral type of M9 on the Boeschaar system. Its evolutionary status is discussed, and we compare it with other objects near the stellar/substellar boundary; owing to the difficult problem of effective temperature calibration for such cool objects comparisons with stellar models are of limited value. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/187786 Bibcode: 1995ApJ...441L..47I Keywords: Astrometry; Astronomical Photometry; Astronomical Spectroscopy; Brown Dwarf Stars; Distance; M Stars; Stellar Luminosity; Stellar Models; Charge Coupled Devices; Chemical Composition; Stellar Parallax; Astrophysics; STARS: LOW-MASS; BROWN DWARFS full text sources ADS | data products SIMBAD (12)

SN 1991F in NGC 3458: A peculiar type IA supernova?

view Abstract Citations (9) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SN 1991F in NGC 3458: A Peculiar Type 1a Supernova Gomez, G. ; Lopez, R. Abstract Supernova 1991F appeared in lenticular galaxy NGC 3458 (UGC 6037). On discovery, it was classified as type I, although no subtype (i.e., Ia or Ib/c) was assigned to it. In this paper, we present several low resolution spectra of this supernova. One of them was recorded ten days after the discovery. No others show the supernova spectral evolution over three months. Our SN 1991F spectra show very close similarities with the spectra of the well studied peculiar supernova 1991bg, which correspond to phases 80-200 days after maximum brightness. We propose that SN 1991F was a peculiar type Ia supernova with similar characteristics to those of the subluminous SN 1991bg. Publication: The Astronomical Journal Pub Date: February 1995 DOI: 10.1086/117316 Bibcode: 1995AJ....109..737G Keywords: Brightness Distribution; Emission Spectra; Evolution (Development); Lenticular Bodies; Supernovae; Astronomical Spectroscopy; Elliptical Galaxies; Magnitude; Astronomy; SUPERNOVAE: INDIVIDUAL: SN 1991F full text sources ADS | data products SIMBAD (10) NED (2)

Young globular clusters in the Milky Way: ARP 2

view Abstract Citations (43) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Young Globular Clusters in the Milky Way: ARP 2 Buonanno, R. ; Corsi, C. E. ; Pecci, F. Fusi ; Richer, H. B. ; Fahlman, G. G. Abstract We have obtained the first B,V CCD color-magnitude diagram (CMD) of the galactic globular cluster Arp 2. About 1600 stars have been measured between the tip of the red giant branch at V approximately 15.5 and V approximately 23.5, about two magnitudes below the main sequence turnoff. A centrally concentrated population of blue stragglers has been detected. The slope of the red giant branch and the overall CMD morphology are consistent with that of a metal-poor cluster, with (Fe/H) = -1.84 +/- 0.25. A preliminary spectroscopic measurement based on the Ca II triplet yields (Fe/H) = -1.73 +/- 0.05. The comparison of the CMD of Arp 2 with that of other clusters favors a value more metal-poor than that indicated by the Ca II triplet. In this respect, Arp 2 is similar to Ruprecht 106. Differential ages between Arp 2 and a number of reference clusters are obtained from the vertical age parameter, deltaHBTO and the horizontal age parameter, delta(B-V)RGBTO By requiring both age estimators to give consistent results, we find that Arp 2 is approximately 3 Gyr younger than the group of the metal-poor clusters and slightly older than Ruprecht 106. The detection of young metal-poor clusters (Fe/H) less than or = -1.8) implies a complex scenario for the origin of the galactic halo, possibly involving interactions with satellite galaxies and their cluster systems. Publication: The Astronomical Journal Pub Date: February 1995 DOI: 10.1086/117308 Bibcode: 1995AJ....109..650B Keywords: Chronology; Color-Magnitude Diagram; Globular Clusters; Milky Way Galaxy; Astronomical Spectroscopy; Blue Stars; Charge Coupled Devices; Galactic Clusters; Galactic Halos; Interacting Galaxies; Metallicity; Morphology; Red Giant Stars; Astronomy; GLOBULAR CLUSTERS: INDIVIDUAL: ARP 2 full text sources ADS | data products SIMBAD (19) CDS (1)

The blue anbd visual absolute magnitude distributions of Type IA supernovae

view Abstract Citations (79) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Blue and Visual Absolute Magnitude Distributions of Type IA Supernovae Vaughan, Thomas E. ; Branch, David ; Miller, Douglas L. ; Perlmutter, Saul Abstract Tully-Fisher (TF), surface brightness fluctuation (SBF), and Hubble law distances to the parent galaxies of Type Ia supernovae (SNs Ia) are used in order to study the SN Ia blue and visual peak absolute magnitude (M_B_ and M_v_) distributions. We propose two objective cuts, each of which produces a subsample with small intrinsic dispersion in M. One cut, which can be applied to either band, distinguishes between a subsample of bright events and a smaller subsample of dim events, some of which were extinguished in the parent galaxy and some of which were intrinsically subluminous. The bright events are found to be distributed with an observed dispersion of 0.3 <~σ_obs_(M) <~0.4 about a mean absolute magnitude (M^bar^_b_ or M^bar^_v_). Each of the dim SNs was spectroscopically peculiar and/or had a red B - V color; this motivates the adoption of an alternative cut that is based on B - V rather than on M. To wit, SNs Ia that are both known to have -0.25 <B - V < +0.25 and not known to be spectroscopically peculiar show observational dispersions of only σ_obs_(M_B_) = σ_obs_(M_V_) = 0.3. Because characteristic observational errors produce σ_err_(M) > 0.2, the intrinsic dispersion among such SNs Ia is σ_int_(M) <= 0.2. The small observational dispersion indicates that SNs Ia, the TF relation, and SBFs all give good relative distances to those galaxies that produce SNs Ia. The conflict between those who use SNs Ia in order to determine the value of the Hubble constant (H_0_) and those who use TF and SBF distances to determine H_0_ results from discrepant calibrations. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/175196 Bibcode: 1995ApJ...439..558V Keywords: Data Reduction; Stellar Magnitude; Supernovae; Astronomical Photometry; Astronomical Spectroscopy; Color-Color Diagram; Color-Magnitude Diagram; Distance; Hubble Constant; Spectrum Analysis; Astrophysics; COSMOLOGY: DISTANCE SCALE; STARS: SUPERNOVAE: GENERAL full text sources ADS | data products NED (96) SIMBAD (91)

H-alpha emission and absorption from a localized region above the surface of a Be star

view Abstract Citations (2) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H alpha Emission and Absorption from a Localized Region above the Surface of a Be Star Marlborough, J. M. Abstract The appearance and disappearance of transient spectral features in the He I line lambda(6678) in the Be star lambda Eri is well established. According to one suggestion these transients arise in a local concentration of matter above the stellar photosphere. In this paper a highly simplified model for the localized region is chosen, and the resultant H-alpha profile from the stellar photosphere and the localized region is obtained for a variety of parameters chosen to span the range of these parameters inferred from analysis of the He I lambda(6678) line. For all the cases investigated the additional H-alpha emission and/or absorption is too weak to be detected easily with present techniques. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/175271 Bibcode: 1995ApJ...440..303M Keywords: Absorption Spectra; B Stars; Emission Spectra; H Alpha Line; Stellar Envelopes; Stellar Models; Stellar Spectra; Astronomical Spectroscopy; Helium; Mathematical Models; Photosphere; Stellar Atmospheres; Visible Spectrum; Astronomy; STARS: CIRCUMSTELLAR MATTER; STARS: EARLY-TYPE; STARS: EMISSION-LINE; BE full text sources ADS | data products SIMBAD (1)

Differential evolution of radio quiet and radio loud quasars

view Abstract Citations (31) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Differential Evolution of Radio Quiet and Radio Loud Quasars Schmidt, Maarten ; van Gorkom, J. H. ; Schneider, Donald P. ; Gunn, James E. Abstract We have observed 40 optically selected high-redshift quasars with the VLA at 1515 MHz (20 cm). Three quasars are detected above our 3σ limit of 0.2 mJy. We review all available evidence on radio detections of optically selected quasars in terms of their ratio R of radio to optical luminosity. We find that the quasars ranked in the top 5-20 percent in R show strong evolution in their R distribution. We present two interpretations of this phenomenon. The first one poses that the R values decrease by a factor of around 100 from redshift 0.3 to 1.3. In the second interpretation, we consider that there are two populations of quasars, which we call radio silent and radio active, separated by R~0.1. The radio-silent fraction of quasars increases from ~16% at redshift 0.3, to ~75% at redshift 1.3. Publication: The Astronomical Journal Pub Date: February 1995 DOI: 10.1086/117292 Bibcode: 1995AJ....109..473S Keywords: Galactic Evolution; Luminosity; Quasars; Radio Astronomy; Radio Observation; Red Shift; Astronomical Spectroscopy; Statistical Analysis; Very Large Array (Vla); Astronomy; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: EVOLUTION; QUASARS: GENERAL full text sources ADS | data products SIMBAD (40) NED (40)