Stellar Spectrophotometry Research Articles

A taste of Fabry and Perot's discoveries

One century ago, Fabry and Perot invented the interferometer which bears their name. The instrument was the culmination of two centuries of related work on light and its interaction with both matter and itself. Today, hundreds of scientists throughout the world use this interferometer daily, perhaps without giving any thought to its ingenious inventors. Fabry and Perot built the instrument, produced theoretical studies and developed methods of analysis; but it was in using it for major scientific discoveries that the instrument would definitively remain synonymous with their names. They studied physics, astronomy and geophysics and strongly contributed to narrowing the gap between physics and astronomy so giving meaning to a new science emerging at the beginning of the century, i.e. astrophysics. Their major works remain the determination of the temperature and kinematics of the Orion nebula, the measurement of the gravitational redshift of light and a contribution to the standard metric system. Other discoveries of theirs are less known: the determination of the altitude and thicknesses of the atmospheric ozone layers; the calibration of the flux of the Moon, the Sun, stars and the Milky Way; the improvement of stellar spectro-photometry; the development of electrometers to measure weak potentials; the elaboration of an atlas of emission lines; the laboratory verification of the Doppler-Fizeau principle and much more.

Ejected Nebulae as Probes of the Evolution of Massive Stars in the Large Magellanic Cloud

We present new Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) and ground-based long-slit spectroscopic observations of the nebulae around the two LMC luminous blue variables (LBVs) R127 (=HDE 269858) and R143 (=HDE 269929) and the Ofpe/WN9 star S119 (=HDE 269687). We have used the ground-based long-slit spectra to investigate the kinematics of the nebulae around R127 and R143. We find that the circumstellar environment of R127 is complex and suggestive of two discrete ejections in the mass loss history of the central star. There is an inner expanding shell, with a radius of 0.6 pc, an expansion velocity of 29 km s-1, and a dynamical age of 2 × 104 yr. There is also material beyond the bright inner nebula that may represent an outer expanding shell with a radius of 1.9 pc and a dynamical age of 7 × 104 yr. For R143, we find that the velocity field in the northern and southern circumstellar regions (1''-20'') is predominantly constant. Therefore, the nebular emission previously believed to be associated with R143 (the fingers) is most likely part of the 30 Doradus complex, with the exception of a small emission-line region located 2'' north of the star. This compact region displays a blueshifted motion with a differential velocity of 130 km s-1 with respect to the central star. The spectrum of this clump shows a high [N II]/Hα ratio, suggestive of nitrogen-enriched material that has been ejected from the star some 3.7 × 103 yr ago. We have used the optical HST/FOS spectra to determine reddenings, electron temperatures and densities, and N and O abundances for the three nebulae. For R143 our derived abundances indicate that the region we observed to the south of the star is 30 Doradus H II gas, since it shows a typical LMC H II region N/O ratio. For R127 we find that N is enriched by a factor of 10.7 ± 2.2, and O is depleted by a factor of 2.0 ± 1.0, with N/O = 0.89 ± 0.40. For the S119 nebula we do not have a secure electron temperature, but find N/O = 1.41-2.45, similar to the value found for R127. We compare the nebular abundances to the expected surface abundances of LBVs and discuss the likely stellar evolutionary state at the time of nebular ejection. If the atmospheres of LBVs consist of CNO-processed material, this implies that the event that formed the nebula took place before or at the very start of the LBV phase. Comparison of the observed nebular abundances with other objects shows that the abundance pattern for the R127 nebula is remarkably similar to that determined for the inner ring of SN 1987A, which is thought to be composed of red supergiant (RSG) wind material. This coincidence, together with the observed low expansion velocity, suggests that the nebula was once the CN-processed convective envelope of an RSG. We consider whether the R127 nebular parameters can be reproduced with the evolutionary models of Meynet et al., and we find that the pre-LBV mass loss has to be low enough for redward evolution such that a surface N/O ~ 1 is achieved while the star is a cool supergiant inside the Humphreys-Davidson limit. Our findings are broadly in accord with the model of Stothers & Chin that incorporates a brief RSG phase. We also consider the possibility of a pseudo-RSG phase by discussing the suggestion that a star in a super-Eddington condition may develop a very extended outer convective envelope that may become detached. We also present a coarse analysis of the FOS stellar spectrophotometry using the Q-method to estimate reddenings and spectral types, and we compare our results to more sophisticated methods.

A new data set for the absolute solar energy distribution in the 310–1070 nm wavelength region

We briefly report on the results of the absolute spectral measurements of solar radiation at the high-mountain station on Peak Terskol, the Caucasus, in 1989 and 1992, including the integral spectrum of the solar disc center, the entire disc, and the brightness temperature of the solar continuum. The fitting of the absolute spectral distribution data for the Sun and Vega with UBV multicolor photometry data is discussed. The results of the solar and stellar spectrophotometry show that the UBV color indices of the Sun must be close to the normal values of the G2V star.

Fundamental spectrophotometry of stars at the astronomical observatory of odessa state university

Abstract We briefly discuss studies of fundamental stellar spectrophotometry at Odessa Astronomical Observatory started in 1967, and the results of star investigations on the basis of stellar spectral energy distributions.

Detection of shocked molecular hydrogen in infrared companions to T Tauri stars: Evidence for ongoing accretion

view Abstract Citations (37) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Shocked Molecular Hydrogen in Infrared Companions to T Tauri Stars: Evidence for Ongoing Accretion Herbst, T. M. ; Koresko, C. D. ; Leinert, Christoph Abstract We report the detection of the 2.12 micrometers, nu = 1-0 S(1) emission line of molecular hydrogen spatially confined to the infrared companions of the Haro 6-10 and UY Aur binary systems. The primaries in both sources appear to be relatively normal pre-main-sequence stars. The K-band spectrum of the Haro 6-10 companion is unusually red and displays no characteristic stellar features. The UY Aur infrared companion, on the other hand, is undoubtedly a star. Our nondetection of the nu = 2-1 S(1) line of H2 implies line ratios inconsistent with a fluorescent origin for the emission and suggests that it is produced by shock heating. These observations strengthen the view that the infrared companions are experiencing ongoing accretion. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/187868 Bibcode: 1995ApJ...444L..93H Keywords: Accretion Disks; Companion Stars; Hydrogen; Infrared Stars; Molecular Spectra; Shock Spectra; Stellar Envelopes; T Tauri Stars; Shock Heating; Speckle Interferometry; Spectral Energy Distribution; Spectrum Analysis; Stellar Spectrophotometry; Astronomy; ACCRETION; ACCRETION DISKS; INFRARED: STARS; STARS: BINARIES: CLOSE; STARS: CIRCUMSTELLAR MATTER; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (5)

The oxygen distribution in NGC 3359 or a disk galaxy in the early phase of bar formation

view Abstract Citations (83) References (62) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Oxygen Distribution in NGC 3359 or a Disk Galaxy in the Early Phase of Bar Formation Martin, Pierre ; Roy, Jean-Rene Abstract Monochromatic imaging in the nebular lines Hα, Hβ, [O III] λ5007, and [N II] λ6584 has been performed on 77 H II regions from 0.13R_eff_ to 2.04R_eff_ in the barred spiral galaxy NGC 3359. The galaxy shows several bright H II regions along its bar; according to numerical simulations of barred galaxies, this morphology suggests that the barred structure was formed recently (within 1 Gyr). The O/H abundance gradient across the disk of NGC 3359 was derived from the abundance indicators [O III]/Hβ and [N II]/[O III] calibrated by Edmunds & Pagel (1984). A break in the slope of the O/H gradient is clearly seen near the corotation radius (~4 kpc). The inner O/H gradient is steep [{DELTA} log (O/H)/{DELTA}R = -0.0701 +/- 0.010 dex kpc^-1^] and the O/H scatter is moderate (+/-0.10 dex); outside the corotation, the gradient appears flat [{DELTA} log (O,/H)/ {DELTA}R = 0.006 +/- 0.018 dex kpc^-1^] and the spread in O/H is significantly larger (+/-0.2 dex) than in the inner parts. This result is in agreement with recent simulations of barred spiral galaxies: star formation inside the corotation radius is enhanced by large amounts of gas driven by radial flows induced by the bar and contributes to maintain the initial O/H gradient; in the outer parts, strong gas mixing induced by flows directed outward and along the spiral arms produces a flattened gradient (e.g., Friedli, Benz, & Kennicutt 1994). Based on previous H I kinematics data on NGC 3359 and results of numerical models of barred galaxies, we show that flows along the spiral arms have had enough time to wiped out the O/H gradient outside the corotation as far as at least 9.5 kpc. However, the presence of large azimuthal abundance fluctuations in the outer disk indicates that the age of the bar is ~4 x 10^8^ yr. The steep inner O/H gradient is also discussed, and we suggest that the present star formation inside the corotation minimizes the dilution of the chemical composition by gas flows. Finally, a brief analysis of the global O/H gradients in disk galaxies with bars showing different star-forming activity is performed. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175682 Bibcode: 1995ApJ...445..161M Keywords: Abundance; Barred Galaxies; Chemical Evolution; Galactic Structure; H Ii Regions; Line Spectra; Oxygen; Star Formation; Corotation; H Lines; Image Analysis; Mathematical Models; Nitrogen; Spectrum Analysis; Stellar Spectrophotometry; Astronomy; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3359; GALAXIES: ISM; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: SPIRAL; GALAXIES: STRUCTURE; ISM: H II REGIONS full text sources ADS | data products SIMBAD (86) NED (10)

Heavy element abundances in a new sample of low-metallicity blue compact galaxies

view Abstract Citations (190) References (77) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Heavy Element Abundances in a New Sample of Low-Metallicity Blue Compact Galaxies Thuan, Trinh X. ; Izotov, Yuri I. ; Lipovetsky, Valentin A. Abstract We present high-quality spectrophotometric observations of 15 supergiant H II regions in 14 new low-metallicity blue compact galaxies (BCGs) selected mainly from the First and Second Byurakan Surveys and with oxygen abundance 12 + log O/H between 7.37 and 8.04 (Z_sun_5/35 <= Z <= Z_sun_/7). We use the data to determine abundances for the elements N, O, Ne, S, Ar, and, for the first time in BCGs, Fe; discuss their origin; and constrain current nucleosynthesis stellar models. The main result of the present study is that none of the heavy element-to-oxygen abundance ratios studied here (N/O, Ne/O, S/0, Ar/O, Fe/O) depend on oxygen abundance. We conclude that all these heavy elements have a primary origin and are produced by the same massive (M >=10 M_sun_) stars. The dispersion of the N/O ratio is found to be remarkably small, being only +/-0.08 in the log. This can only be understood if primary N is produced in massive stars, not in intermediate-mass (4 M_sun_ <= M <= 9 M_sun_) stars as commonly thought. BCGs show the same O/Fe overabundance with respect to the Sun (~0.34 in the log) as galactic halo stars, suggesting the same chemical enrichment history, and supporting the scenario of an early enrichment of the galactic halo by massive Population III stars. We have compared the observed heavy element abundance ratios with theoretical yields from current massive star nucleosynthesis models from Weaver & Woosley (1993). The small dispersion in the heavy element abundance ratios suggests that there is not a large IMF variation between BCGs with different metallicities. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175676 Bibcode: 1995ApJ...445..108T Keywords: Abundance; Compact Galaxies; H Ii Regions; Heavy Elements; Line Spectra; Massive Stars; Nuclear Fusion; Sky Surveys (Astronomy); Argon; Flux Density; Neon; Nitrogen; Oxygen; Spectrum Analysis; Stellar Spectrophotometry; Sulfur; Astronomy; GALAXIES: ABUNDANCES; GALAXIES: COMPACT; ISM: H II REGIONS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES full text sources ADS | data products SIMBAD (22) NED (14)

Activity cycles in cool stars. 1: Observation and analysis methods and case studies of four well-observed examples

view Abstract Citations (7) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Activity Cycles in Cool Stars. I. Observation and Analysis Methods and Case Studies of Four Well-observed Examples Hall, Jeffrey C. ; Lockwood, G. W. ; Gibb, Erika L. Abstract This is the first in a series of papers devoted to the ongoing long-term monitoring program of activity cycles in cool stars at Lowell Observatory. In this paper we discuss the various spectral diagnostics we have at our disposal and how we calibrate these diagnostics to flux. We then present our current database for four well-studied stars, HD 10700, HD 22049, HD 39587, and the Sun, comparing our results to results obtained by other investigators and discussing how our new database complements existing work. With the same data we demonstrate our ability to detect activity cycles and rotational modulation in a variety of diagnostic lines for stars of widely differing activity levels and spectral types. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175483 Bibcode: 1995ApJ...442..778H Keywords: Cool Stars; Data Bases; Late Stars; Spectrum Analysis; Stellar Rotation; Stellar Spectra; Stellar Spectrophotometry; Continuous Spectra; Data Reduction; H Alpha Line; Numerical Analysis; Astronomy; STARS: ACTIVITY; STARS: LATE-TYPE; STARS: ROTATION full text sources ADS | data products SIMBAD (12)

Rapid H-alpha emission variations in accretion disks in long-period ALGOLS

view Abstract Citations (15) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rapid H(alpha) Emission Variations in Accretion Disks in Long-Period ALGOLS Olson, Edward C. ; Etzel, Paul B. Abstract We demonstrate the continuous presence of large variations in double-peaked H-alpha long period Algol-type binaries, using recently obtained CCD spectra. Most fluctuations occur on a time scale less than or = an orbital period and a steady state in H-alpha emission ia never reached. In AD Her (P = 10 d), H-alpha emission dropped in strength more than a factor of five in one seven-day interval. Contemporay O I lambda observations showed no significant changes in oxygen absorption strength or radial velocity during this time. We tentatively suggest that H-alpha variations arise from an inner-disk instability, possibly triggered by small modulations in the mass-transfer rate. This behavior is reminiscent of some cataclysmic variables. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117362 Bibcode: 1995AJ....109.1308O Keywords: Accretion Disks; Eclipsing Binary Stars; H Alpha Line; Mass Flow Rate; Stability; Stellar Orbits; Variability; Charge Coupled Devices; Radial Velocity; Spectrum Analysis; Stellar Spectrophotometry; Astronomy; BINARIES: SPECTROSCOPIC; CIRCUMSTELLAR MATTER; ACCRETION DISKS full text sources ADS | data products SIMBAD (11) CDS (1)

Spectroscopy of evolved stars in the near infrared: Explorations beyond the AGB

view Abstract Citations (20) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy of Evolved Stars in the Near Infrared: Explorations Beyond the AGB Kelly, Douglas M. ; Latter, William B. Abstract We present spectra taken between lambda = 0.9 - 1.3 micrometers for a sample of evolved stars ranging from Mira variable stars to planetary nebulae. An evolution can be seen from the absorption spectra of the late-type stars to the emission line spectra of the planetary nebulae. We compare emission line strengths for objects ranging from Teff = 30 000 to 200 000 K, and we use infrared and visible line ratios to determine densities and temperatures in the emission line regions. We examine the four factors that are most important to determining relative ion strengths-stellar temperature, evolutionary status, excitation mechanism, and clumpiness. It is found that clumps appear to be common, and that shocks are very important to the excitation and shaping of planetary nebulae, We also find that the strength of the low ionization and molecular emission lines decreases with age, and we use a filling factor analysis to show that this evolution is caused by a decrease in the amount of low ionization material close to the star. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117364 Bibcode: 1995AJ....109.1320K Keywords: Infrared Spectra; Ion Density (Concentration); Late Stars; Planetary Nebulae; Stellar Evolution; Stellar Temperature; Visible Spectrum; Absorption Spectra; Abundance; Emission Spectra; Spectrum Analysis; Stellar Spectrophotometry; Vibrational Spectra; Astronomy; STARS: POST-ASYMPTOTIC GIANT BRANCH; PLANETARY NEBULAE: GENERAL; ISM: GENERAL full text sources ADS | data products SIMBAD (25)

Cataclysmic and close binaries in star clusters. 2: Probing the core of NGC 6752 with Hubble Space Telescope

view Abstract Citations (33) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cataclysmic and Close Binaries in Star Clusters. II. Probing the Core of NGC 6752 with Hubble Space Telescope Shara, Michael M. ; Drissen, Laurent ; Bergeron, Louis E. ; Paresce, F. Abstract The cores of globular clusters have been predicted to be rich in close, interacting binaries. We have used the Hubble Space Telescope (HST) to test this prediction by monitoring 730 stars in the core of NGC 5752 for rapid variability. Thirty-one Faint Object Camera (FOC) images at 2200 A, with time resolution of 11 minutes, and spanning 7 hr have been searched for variables. Artificial star tests demonstrate that we should have found virtually all variables brighter than m2200 = 20 (i.e., M220 less than or = 6.75) with variability amplitude Delta m greater than or = 0.25 mag and most variables brighter than m2200 = 22 (i.e., M2200 less than or = 8.75) with Delta m greater than or = 0.35 mag. No variables were found; eight were expected based on tidal capture models in the one-fourth of the core that we observed. Our results strongly constrain the number of cataclysmic and contact binaries (with the above variability and luminosity limits) in the core of NGC 6752 to be less than or = 10 in total with 95% probability. A color-magnitude diagram reveals the presence of four UV-excess stars below the turnoff, all located within 6 arcsec of the cluster center. None show detectable variability (sigma less than or = 0.1 mag) during the 7 hr FOC observing sequence. Two of them are detected in archival HST planetary camera (PC) R and H-alpha images, but show no H-alpha excess. The lack of variability, the absence of H-alpha emission, as well as the fact that none of them appear in outburst in any of four epochs, strongly suggest that they are not cataclysmic variables. This is the strongest observational test to date of simple tidal capture theory. NGC 6752 appears to have significantly fewer tidal capture binaries than the simple tidal capture theory predicts. Five blue stragglers are discovered, as well as 14 horizontal-branch stars which completely dominate the cluster light at 2200 A. The main sequence luminosity function of NGC 6752 is remarkably flat at the cluster center. This is in contrast to the rising value found by Da Costa at 10.1 arcmin less than or = r less than 13.2 arcmin and Richer et al. at 6 arcmin less than or = r less than 10 arcmin. Mass segregation probably accounts for the difference. The preponderance of low-mass stars in the outer parts of NGC 6752 may be due to enrichment (i.e., depletion of the core and transport outward of these low-mass stars) rather than being primordial. If this is true, then the suggestion that dissolved globular cluster low-mass Population II stars may be an important component of the mass budget of the Galactic halo is further weakened. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175387 Bibcode: 1995ApJ...441..617S Keywords: Cataclysmic Variables; Eclipsing Binary Stars; Globular Clusters; Image Analysis; Spaceborne Astronomy; Color-Magnitude Diagram; Faint Object Camera; Hubble Space Telescope; Light Curve; Main Sequence Stars; Stellar Luminosity; Stellar Spectrophotometry; Astronomy full text sources ADS | data products SIMBAD (6) MAST (1) ESA (1) Related Materials (3) Part 1: 1994ApJ...429..767S Part 3: 1995ApJ...448..203S Part 4: 1996ApJ...471..804S

CCD photometry for the galactic globular cluster NGC 6584

view Abstract Citations (31) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CCD Photometry for the Galactic Globular Cluster NGC 6584 Sarajedini, Ata ; Forrester, Wendy L. Abstract We present CCD photometry in the B and V passbands for the Galactic globular cluster NGC 6584. The color-,agmotide diagram reveals a horizontal branch (HB) populated on both the red and blue sides of the RR Llyrae instability strip. The cluster contains 42 confirmed RR Lyrae variables, and we find an additional 56 stars which are possible RR Lyraes. The mean magnitude of the RR Lyraes on our CCD frames is combined with that of the nonvariable stars to yield (V(HB)) = +/- 0.03. Using a polynomial fit to the cluster giant stars, we derive the color of the giant branch at the level of the HB to be (B-V)g = 0.89 +/- 0.02. Our photometry has also been used to isolate the red giant branch clump which forms when stars pause and sometimes reverse their course as they evolve up the giant branch. Its luminosity is primarily dependent upon the cluster metallicity, and we have used this fact to derive a metallicity of (Fe/H = -1.44 +/- 0.16 for NGC 6584. Coupled with the color of the giant branch given above, this yields a cluster reddening of E)B-V) = 0.07 +/- 0.04. To the extent that our photometry can be used to study the age of NGC 6584, we find it to be comparable to M3, which is not surprising given their similar HB morphologies. The color-magnitude diagram also exhibits a significant population of blue straggler stars. From a comparison of the blue straggler radial distribution to that of the subgiant stars with similar V magnitudes, we find that the blue stragglers are more centrally concentrated than the subgiants, indicative of a higher mass for the blue stragglers. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117345 Bibcode: 1995AJ....109.1112S Keywords: Globular Clusters; Horizontal Branch Stars; Metallicity; Red Giant Stars; Stellar Color; Stellar Magnitude; Subgiant Stars; Variable Stars; Charge Coupled Devices; Chronology; Color-Magnitude Diagram; Radial Distribution; Star Distribution; Stellar Spectrophotometry; Astronomy; GLOBULAR CLUSTERS: INDIVIDUAL: NGC 6584; GALAXY: HALO; GALAXY: ABUNDANCES full text sources ADS | data products SIMBAD (6) CDS (1)

The globular cluster system of M81

view Abstract Citations (65) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Globular Cluster System of M81 Perelmuter, Jean-Marc ; Racine, Rene Abstract We have obtained photometric BVR, morphological, and astrometric information on 3774 objects located within a 25' radius of M81. This catalogue is complete for 15 <= V <= 21; it is used here to identify globular cluster candidates in M81 and as a database for a statistical analysis of the system as a whole. The M81 globular cluster system is revealed as a strong surface density excess of ~70 objects within an 11 kpc galactocentric radius. The total population is estimated at N_T_ = 210 +/- 30 globulars. The spatial, (B-V), and (V-R) distributions are very similar to those of the Milky Way and of M31. Small but significant systematic errors in Madore et al.'s (AJ, 106, 2243 (1993)] photometry could be responsible for an overestimate of the Cepheid distance to M81 [(m -M)_0_ = 27.8] and we propose a revised modulus of (m-M)_0_ = 275 +/- 0.3. The globular cluster luminosity function then reaches its maximum at M_V_^*^ = - 7.5 +/- 0 4 as it does in the galaxy and in M31. There is suggestive evidence that 13+/-5 objects are globulars seen through the disk of M81; spectroscopy or high-resolution imaging will resolve this issue. Using the (B - R)_0_ index to trace [Fe/H], we notice a weak dependence of mean metallicity on galactocentric distance, as observed in the galaxy and in M31. This result argues in favor of in situ globular formation during the continuous collapse and self-enrichment of an early-type spiral host. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117341 Bibcode: 1995AJ....109.1055P Keywords: Astrometry; Distance; Globular Clusters; Metallicity; Populations; Spatial Distribution; Spiral Galaxies; Stellar Luminosity; Calibrating; Color-Color Diagram; Color-Magnitude Diagram; Errors; Image Analysis; Interstellar Extinction; Stellar Motions; Stellar Spectrophotometry; Astronomy; GALAXIES: INDIVIDUAL: M81; GLOBULAR CLUSTERS: GENERAL; GALAXIES: NUCLEI full text sources ADS | data products NED (3588) SIMBAD (1327) CDS (1)

Photoelectric UBVRI sequences in the galactic globular clusters NGC 5286, NGC 5927, and NGC 6541

view Abstract Citations (5) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photoelectric UBVRI Sequences in the Galactic Globular Clusters NGC 5286, NGC 5927, and NGC 6541 Alvarado, Franklin ; Wenderoth, Erich ; Alcaino, Gonzalo ; Liller, William Abstract UBVRI photoelectric sequences for three low-latitude galactic globular clusters. NGC 5286, NGC 5927, and NGC 6541, are presented herein. All include fields suitable for CCD coverage. The number of stars and the range of magnitudes and colors are; NGC 5286, 8 stars with 13.6 less than V less than 15.3, 0.6 less than B - V less than 1.3; NGC 5927, 11 stars with 11.3 less than V less than 14.9, 0.3 less than B - V less than 1.6; NGC 6541, 16 stars with 12.2 less than V less than 15.7, 0.2 less than B - V less than 1.6. The stars were measured an average of seven times on at least five different nights. To the best of our knowledge, none of these stars have UBVRI photoelectric measurements reported by other authors. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117349 Bibcode: 1995AJ....109.1169A Keywords: Globular Clusters; Stellar Color; Stellar Magnitude; Calibrating; Data Reduction; Interstellar Extinction; Photoelectric Emission; Stellar Spectrophotometry; Astronomy; GLOBULAR CLUSTERS: GENERAL; GALAXY: HALO; GALAXY: ABUNDANCES full text sources ADS | data products SIMBAD (39) GCPD (1) CDS (1)

The unusual morphology of molecular hydrogen emission in the planetary nebula J900

view Abstract Citations (11) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Unusual Morphology of Molecular Hydrogen Emission in the Planetary Nebular J900 Shupe, D. L. ; Armus, L. ; Matthews, K. ; Soifer, B. T. Abstract We report new high-resolution near-infrared imaging observations of the planetary nebula J900, in broadband J, H, and K, and narrowband 2.122 micrometers (for H2 1-0 S(1)), Brackett-gamma, and continuum filters. The H2 images reveal a remarkable set of outward-extending features not detected in any previous observations of theis object. In the northwest lobe of the inner bipolar region, the H2 emission, Brackett-gamma emission, and underlying continuum are spatially resolved. The relative positions of the peaks of the line emission suggest an ionization front seen edge-on. The continuum emission, apparently located nearer to the central star, is likely due to transiently heated small dust grains. The extended H2 emission features are probably excited either by oblique shocks caused by material ejected from the nebula, or by radiation leaking from holes in the opacity surrounding the ionized shell. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117350 Bibcode: 1995AJ....109.1173S Keywords: Hydrogen; Infrared Imagery; Morphology; Planetary Nebulae; Stellar Envelopes; Stellar Winds; Vibrational Spectra; Flux Density; Image Analysis; Ionization; Shock Fronts; Spatial Resolution; Stellar Spectrophotometry; Astronomy; PLANETARY NEBULAE: INDIVIDUAL: J900; ISM: JETS AND OUTFLOWS full text sources ADS | data products SIMBAD (5)

Photometric discriminate for GK dwarfs of disk populations

view Abstract Citations (7) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric Discriminate for GK Dwarfs of Disk Populations Eggen, Olin J. Abstract The young and old disk populations, with ages respectively less than and greater than about 2 x 109 yr, are separated in the (R - I, 42 - 45) plane, where the 42 - 45 index of the DDO system is based on bandpasses of 75 A half-width and effective wavelengths of 4257 and 4571 A. A similar, but smaller separation is seen in the (g,B2 - VI) plane where g is the Geneva system alternative to 42 - 45 but with bandpasses of 175 A half-width and effective wavelengths of 4015 and 4476 A. Although models, based on the assumption that this separation results from a veil of weak metal lines (Magain 1983), may explain these phenomena in the (g,B2 - VI) plane for the hotter stars, more models are required to test it for the DDO system and for cooler objects. The available evidence suggests that an additional causation, probably connected with the CN abundance, also exists. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117365 Bibcode: 1995AJ....109.1327E Keywords: Abundance; Dwarf Stars; Main Sequence Stars; Star Clusters; Stellar Color; Stellar Evolution; Stellar Gravitation; Stellar Magnitude; Absorptance; Color-Color Diagram; Color-Magnitude Diagram; Data Reduction; Metallicity; Stellar Spectrophotometry; Astronomy; GALAXY: STELLAR CONTENT; STARS: PECULIAR; STARS: EVOLUTION full text sources ADS | data products SIMBAD (203)

Be Ursae Majoris: Precataclysmic binary system and planetary nucleus

view Abstract Citations (33) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS BE Ursae Majoris: Precataclysmic Binary System and Planetary Nucleus Liebert, James ; Tweedy, R. W. ; Napiwotzki, R. ; Fulbright, M. S. Abstract This paper presents new spectrophotometric observations and a new analysis of the hot and cool components of the evolved binary system BE Ursae Majoris, and we report the discovery of a planetary nebula around it. The primary star can be classified as a subdwarf O or borderline DAO white dwarf with Teff = 105,000 K +/- 11,000 K, log g = 6.5 +/- 0.25, based on Non Local Thermodynamic Equilibrium (NLTE) model atmosphere profile fits to the H and He II lines. Observations of the secondary during eclipse indicate a spectral type of K5. Its estimated brightness during eclipse is consistent with a main-sequence star of K5 at the distance of 1.9 kpc derived from analysis of the primary star. The nebula is roughly circular with a diameter of 3 min. This corresponds to a physical diameter of 1.5 pc at the estimated distance. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175366 Bibcode: 1995ApJ...441..424L Keywords: Cataclysmic Variables; Eclipsing Binary Stars; K Stars; Planetary Nebulae; White Dwarf Stars; Atmospheric Models; Local Thermodynamic Equilibrium; Stellar Models; Stellar Spectrophotometry; Astronomy full text sources ADS | data products SIMBAD (1)

Washington photometry of the globular cluster system around NGC 3311. 1: Analysis of the metallicities

view Abstract Citations (49) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Washington photometry of the globular cluster system around NGC 3311. I. Analysis of the metallicities. Secker, Jeff ; Geisler, Doug ; McLaughlin, Dean E. ; Harris, William E. Abstract We have obtained metal abundances from Washington photometry (C, T1) for a large sample of globular clusters around NGC 3311, the central cD in the Hydra I (A1060) galaxy cluster. Our spatial coverage extends out to a galactocentric radius approximately 2.2 arcmin (about 30 kpc for H0 = 75). Analysis of the metallicity distribution function (MDF) reveals a median metallicity of (Fe/H)C-T1 = -0.31 with a dispersion of 0.35 dex; the MDF is skewed, with a small but definite low-metallicity tail extending down to (Fe/H)C-T1 approximately -1.8 dex. It may also be bimodal, with significant peaks near (Fe/H)C-T1 = -0.5 and 0.15 dex. We estimate that 30 percent of the clusters exceed solar abundance, based upon a linear extrapolation of the galactic calibrating relation between (c-T(sub1))0 and (Fe/H)C-T1. Perhaps most notably, the population of clusters near (Fe/H)C-T1 approximately -1 that dominates the MDF in order giant E galaxies is almost totally missing in NGC 3311 making it the most metal-rich system known. Finally, we find a significant radial gradient in mean metallicity, Delta (Fe/H)C-T1/ Delta (log Rgc = -0.78+/-0.60. It is suggested that virtually all the protostellar gas in this cD galaxy went through a considerable amount of pre-enrichment everywhere in the halo, before almost any stars or clusters formed. These data provide a strong challenge to any model which requires low metallicity for globular cluster formation. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117338 Bibcode: 1995AJ....109.1019S Keywords: Abundance; Galactic Halos; Globular Clusters; Metallicity; Star Formation; Stellar Color; Stellar Composition; Stellar Luminosity; Color-Magnitude Diagram; Data Reduction; Spatial Distribution; Stellar Spectrophotometry; Astronomy full text sources ADS | data products SIMBAD (119) NED (1) Related Materials (1) Part 2: 1995AJ....109.1033M

Radial velocities of very low mass stars and candidate brown dwarf members of the Hyades and Pleiades, 2

view Abstract Citations (35) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radial Velocities of Very Low Mass Stars and Candidate Brown Dwarf Members of the Hyades and Pleiades. II. Stauffer, John R. ; Liebert, James ; Giampapa, Mark Abstract We have determined H alpha equivalent widths and radial velocities with 1 sigma accuracies of approximately 5 km/s for approximately 20 candidate very low mass members of the Pleiades cluster and for a few proposed very low mass members of the Hyades. Most of the Pleiades targets were selected from the recent Hambly, Hawkins, and Jameson proper motion survey, where they were identified as probable Pleiades brown dwarfs with an age spread from 3 to 70 Myr. Our spectroscopic data and a reinterpretation of the photometric data confirm that these objects are indeed likely Pleiades members; however, we believe that they more likely have masses slightly above the hydrogen burning mass limit and that there is no firm evidence for an age spread amongst these stars. All of the very low mass Pleiades and Hyades members show H alpha in emission. However, the ratio of H alpha flux to biometric flux in the Pleiades shows a maximum near MBol approximately equal to 9.5 (M approximately equal to 0.3 solar mass) and a sharp decrease to lower masses. This break occurs at the approximate mass where low mass stars are expected to become fully convective, and it is tempting to assume that the decrease in H alpha flux is caused by some change in the behavior of stellar dynamos at this mass. We do not see a similar break in activity at this mass in the Hyades. We discuss possible evolutionary explanations for this difference in the H alpha activity between the two clusters. Publication: The Astronomical Journal Pub Date: January 1995 DOI: 10.1086/117273 Bibcode: 1995AJ....109..298S Keywords: Brown Dwarf Stars; H Alpha Line; Pleiades Cluster; Radial Velocity; Stellar Mass; Stellar Evolution; Stellar Spectrophotometry; Astrophysics; OPEN CLUSTERS AND ASSOCIATIONS: GENERAL; STARS: LOW MASS; STARS: BROWN DWARFS full text sources ADS | data products SIMBAD (35)

The optical and near-infrared colors of galaxies. 2: Spectral classification

view Abstract Citations (40) References (86) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical and Near-Infrared Colors of Galaxies. II. Spectral Classification Bershady, Matthew A. Abstract We have used optical and near-infrared photometry of a well defined sample of field galaxies with spectroscopic redshifts [Bershady et al., 108, 870 (1994)] to study and characterize the trends and dispersions of rest-frame colors at intermediate redshifts of z <= 0.3. We have constructed a simple spectral synthesis model which serves to determine the information available in our five bands (U, J, F, N, and K) to constrain the stellar composition of galaxies, as well as to classify spectrally our sample. We find that a simple model consisting of two stellar spectral types can reproduce well the observed broadband colors, but only if the types are allowed to vary. The five primary galaxy spectral types resulting from this model are bk, bm, am, fm, and gm (lower-case letters refer to stellar types B, K, etc.), and are distinct both in stellar type and mixture. The hottest galaxy spectral types have a very narrow range of stellar fractions, whereas the cooler types show a broader range of stellar fractions that are qualitatively consistent with more sophisticated stellar population synthesis models of similar stellar systems. Two types, am and fm, have similar rest-frame colors, although am-type galaxies are on average 2.5 times more luminous. We describe how our spectral synthesis model, when fit to the observed colors of galaxies, provides an accurate interpolative means for determining rest- frame colors. The κ-corrections calculated in this way are consistent with more sophisticated models and observed spectral energy distributions of local galaxies. Spectral classification is well suited for the study of distant galaxies because of the direct connection between spectral type and κ-correction. κ-corrections for the K band, however, are shown to be very uniform for all galaxy types to z = 0.3, as predicted by models. The mean K band κ-corrections are tabulated as a function of redshift. Luminosities in all bands are also tabulated for individual galaxies. The rest-frame color distributions of our galaxies are comparable in range to local samples; there are no new spectral types at the intermediate redshifts and magnitude limits of our sample. In the U- V, V-K two-color plane, the trend of the rest-frame colors with galaxy spectral type well matches the mean distribution of local galaxies binned by morphological type. Particular attention is paid, however, to the scatter in these colors. Color-luminosity effects are observed in both V-K and U-V for all galaxy types over a combined range of 10 magnitudes. The range of colors at a fixed absolute magnitude is comparable to the change in mean color over the observed absolute magnitude range. In contrast to studies of galaxies segregated by Hubble type, we find no evidence for a strong galaxy spectral type dependence on the slope of the color-luminosity correlation. If physical parameters, such as age and metallicity give rise to the relationship between color and luminosity, they must conspire to produce similar effects for all galaxy spectral types. Publication: The Astronomical Journal Pub Date: January 1995 DOI: 10.1086/117259 Bibcode: 1995AJ....109...87B Keywords: Galaxies; Infrared Photometry; Spectrum Analysis; Stellar Color; Astronomical Models; Broadband; Color-Color Diagram; Extremely High Frequencies; Luminosity; Red Shift; Stellar Spectrophotometry; Astronomy; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: FUNDAMENTAL PARAMETERS full text sources ADS | data products SIMBAD (177) NED (173) Related Materials (1) Part 1: 1994AJ....108..870B