CCD Spectra Research Articles

The Temperature Scale and Mass Distribution of Hot DA White Dwarfs

Results are presented from a comprehensive spectroscopic survey of DA white dwarfs hotter than ~25,000 K. The observations consisted of CCD spectra with signal-to-noise ratios of ~100 in the blue, with ~5 Å resolution. The majority of the spectra covered the wavelength range of 3500-7500 Å, allowing the detection of a number of cool companions. To date, spectra have been obtained and analyzed for 174 DA stars. The spectra were analyzed using our model atmospheres, which are described in detail here, resulting in temperatures and gravities with average internal errors of 1% and 0.04 dex, respectively. Comparisons with previously published results showed that temperature determinations for Teff < 30,000 K were generally consistent at the 1% or better level, while spectroscopic gravity determinations based on the latest models were consistent at the 0.02 dex level. Wood's evolutionary sequences were used to derive masses for the observed stars with average internal errors of 0.02 M☉. The mass distribution for this hot sample peaked at 0.570 M☉, consistent with previous spectroscopic results for cooler samples.

Spectroscopic Study of C, N, O, and S Abundances in a Field Horizontal-Branch Star HD 161817

A detailed non-LTE analysis of neutral C, N, O, and S lines was performed based on a set of CCD spectra in the red and near-IR wavelength regions for a field Pop II horizontal-branch star HD 161817 (along with 20 CVn included for a comparison), in order to establish the photospheric abundances of these elements. It turned out that [O/Fe] and [S/Fe] show a mild excess, amounting to 0.4–0.5 dex, which agrees quantitatively well with that of typical halo dwarfs corresponding to [Fe/H] ∼ –1.5 (the metallicity of HD 161817), suggesting that the original composition is retained unaltered for oxygen and sulfur (α-elements). Meanwhile, the resulting abundances of carbon and nitrogen ([C/Fe] ∼ −0.2 and [N/Fe] ∼ +0.5) indicate a mixing of CN-cycle products, when compared with [C/Fe] =≃ [N/Fe] ≃ 0 (a typical value occasionally quoted for dwarfs in the halo). It was also found that the microturbulent velocity tends to increase with height in the atmosphere of HD 161817, which may be the cause for the discrepancy between the value established from blue metallic lines (2–3 km s−1) and that from OI 7771–5 (4 km s−1).

GALACTIC GLOBULAR CLUSTER METALLICITY SCALE FROM THE CA II TRIPLET I. CATALOG

ABSTRACT We have obtained 2640 CCD spectra with resolution ∼4~Å\\ in the region 7250--9000~Å\\ for 976 stars lying near the red giant branches in color-magnitude diagrams of 52 Galactic globular clusters. Radial velocities of ∼16 \\kms\\ accuracy per star determined from the spectra are combined with other criteria to assess quantitative membership probabilities. Measurements of the equivalent widths of the infrared calcium triplet lines yield a relative metal-abundance ranking with a precision that compares favorably to other techniques. Regressions between our system and those of others are derived. Our reduction procedures are discussed in detail, and the resultant catalog of derived velocities and equivalent widths is presented. The metal abundances derived from these data will be the subject of a future pape.

The Ca II triplet lines as diagnostics of luminosity, metallicity and chromospheric activity in cool stars

CCD spectra of the infrared triplet lines of ionized calcium at 8498, 8542, 8662 have been obtained at a spectral resolution of 0.4 Ain 146 stars brighter than spanning a range in spectral types from F7 to M4 of all luminosity classes and a range in metallicity [Fe/H] from -3.0 to +1.1. These have been analysed to investigate the dependence of the Ca II triplet strengths on stellar parameters like luminosity, temperature and metallicity. A detailed study reveals a strong dependence on luminosity, much stronger for metal rich stars than for the metal poor ones and a milder dependence on metallicity, although much more conspicuous in supergiants than in dwarfs. All these correlations are found to be non-linear over the parameter space covered. The present study also shows chromospheric activity to be an important phenomenon affecting the strength and the shape of the line profiles. Stars of similar luminosity and metallicity have varying Ca II line depths owing to varying chromospheric emission filling in their Ca II absorption. The Ca II triplet strength is thus observed to be a triparametric discriminant in cool stars.

THE ANGULAR MOMENTUM OF MAIN SEQUENCE STARS AND ITS RELATION TO STELLAR ACTIVITY

ABSTRACT Rotational velocities are reported for intermediate-mass main sequence stars it the field. The measurements are based on new, high S/N CCD spectra from the Coudé Feed Telescope of the Kitt Peak National Observatory. We analyze these rotation rates for a dependence on both mass and age. We compare the average rotation speeds of the field stars with mean velocities for young stars in Orion, the Alpha Persei cluster, the Pleiades, and the Hyades. The average rotation speeds of stars more massive than ∼1.6 M⊙\\experience little or no change during the evolutionary lifetimes of these stars on the zero age main sequence or within the main sequence band. Less massive stars in the range betwee n 1.6M⊙\\ and 1.3M⊙\\ also show little decline in mean rotation rate while they are on the main sequence, and at most a factor of 2 decrease in velocity as they evolve off the main sequence. The {e}-folding time for the loss of angular momentum b y the latter group of stars is at least 1--2 billion years. This inferred characteristic time scale for spindown is far longer than the established rotational braking time for solar-type stars with masses below ∼1.3 M⊙. We conclude from a comparison of the trends in rotation with trends in chromospheric and coronal activity that the overall decline in mean rotation speed along the main sequence, from ∼2 M⊙\\ down to ∼1.3 M⊙, is imposed during the pre-main sequence phase of evolution, and that this pattern changes little thereafter while the star resides on the main sequence. The magnetic activity implicated in the rotational spindown of the Sun and of similar stars during their main sequence lifetimes mus t therefore play only a minor role in determining the rotation rates of the intermediate mass stars, either because a solar-like dynamo is weak or absent, or else the geometry of the magnetic field is appreciably less effective in removing angular momentu m from these stars.

An abundance analysis of the single-lined spectroscopic binaries with barium stars-like orbital elements

Detailed abundance analyses have been car- ried out for 17 single-lined binaries (giants and dwarfs) with orbital elements and mass functions similar to those of barium stars, using high-dispersion CCD spectra and model atmospheres. All these binary systems contain an unseen low-mass component, presumably, a white dwarf. A mild enhancement (+0:1 0:25 dex) of the averaged s- process elements abundances has been found only for two stars. The heavy-element overabundances in these stars are much less marked than those of the classical barium stars having similar orbital periods. We have concluded that the existence of a white dwarf (WD) companion in binary systems with barium star like characteristics is not sucient to produce a strong barium star. However, ve of the analyzed giants show a signicant enhancement (0:2 0:3 dex) of barium. The analysis indicates that a main sequence companion has not a signicant influ- ence (due to tidal mixing, as has been sometimes sug- gested) on the internal structure (chemical composition) of the primary star. Since barium enhanced giants occupy a place on the (eccentricity-orbital period) plane similar to BaII stars we have concluded that a mild barium enhance- ment in these stars is due to mass transfer from the com- panion during its late phases of evolution. Thus it seems likely that all giants (primaries) in barium star like binary systems with WD component have chemical peculiarities (very slight in some cases) depending, apparently, on the eciency of mass transfer in a specic binary system. The signicant enhancement of heavy elements in the atmo- spheres of two radial velocity non-variable barium stars

SPECTROSCOPIC OBSERVATIONS OF SOME BE/B STARS AT HIGH GALACTIC LATITUDES

ABSTRACT Spectral types, rotational velocities, and radial velocities were estimated for eight Be and two non-emission B stars at high galactic latitudes from CCD spectra, and their distances from the galactic plane calculated. All of the objects appear to be spectroscopically normal; for the Be stars, at least, there is no reason to evoke an unusual origin for this sample of stars.

Abundances for globular cluster giants. I. Homogeneous metallicities for 24 clusters

We have obtained high-res, high S/N ratio CCD echelle spectra of 10 bright red giants in 3 GCs (47Tuc, NGC6752 and NGC6397) roughly spanning the range of metallicities of the galactic GC system; they reveal no evidence of star to star variation of [Fe/H] in these 3 GCs. A large set of high quality literature data (EWs from high-res CCD spectra) was re-analyzed in a self-consistent way to integrate our data and derive new [Fe/H] for more than 160 bright red giants in 24 GCs. This set was used to define a new [Fe/H] scale for GCs based on high quality, direct spectroscopic data, on updated model atmospheres from the grid of Kurucz (1992) and on a careful fine abundance analysis (using a common set of atomic and atmospheric parameters for all stars). Given the high internal homogeneity, our new scale supersedes the discrepancies of previous attempts. The internal uncertainty in [Fe/H] is very small: 0.06 dex (24 GCs) on average, that can be interpreted as the mean precision of cluster ranking. Compared to our system, metallicities on the widely used Zinn and West's scale are about 0.10dex higher for [Fe/H]$>-1$, 0.23dex lower for $-1<[Fe/H]<-1.9$ and 0.11dex too high for [Fe/H]$<-1.9$: the non-linearity is significant at 3$\sigma$ level. A quadratic transformation corrects older values to the new scale in the range of our calibrating GCs ($-2.24\le[Fe/H]_{ZW}\le-0.51$). A minor disagreement is found at low [Fe/H] between the metallicity scale based on field and cluster RR Lyrae's (via a new calibration of the $\Delta$S index) and our new GCs metallicities, that could be ascribed to non-linearity in the [Fe/H]$-\Delta$S relationship. The impact of new metallicities on major astrophysical problems is exemplified through the Oosterhoff effect in the classical pair M3 and M15.

A newH ? survey of chromospherically active binaries (II)

We have obtained CCD spectra for 30 chromospherically active binaries using the 2.16 m telescope at Beijing Observatory in 1995. Our purpose was to search for the presence ofHα emission which is characteristic of stars with extreme levels of chromospheric activity. Spectra of V711 Tau, V471 Tau, HD 12545 and V833 Tau presentedHα emission above the continuum in the different degree. TheHα behavior of the other observed 26 active binaries, which were unknown in CABS (1993), has been discovered in this paper. TheHα profiles of the most among 26 systems are partially filled-in by chromospheric emission. TheHα profiles of a few systems show a pure absorption line. The results are given in Table I.

Identification of Supernova Remnants in the Sculptor Group Galaxies NGC 300 and NGC 7793

We have obtained CCD imagery of eight fields in the Sculptor Group Sc spiral galaxy NGC 300 and two fields covering the Sculptor Sd spiral galaxy NGC 7793, using interference filters to isolate emission from Hα + [N II], [S II], and a continuum band near 6100 A. Using these images, we have identified isolated nebulae that are bright in [S II] relative to Hα, indicating probable shock heating, and that have morphologies consistent with identification as supernova remnants (SNRs). Our lists of candidates contain 28 objects each in NGC 300 and NGC 7793. We then obtained optical (4800-6900 A) long-slit CCD spectra of many of these nebulae, as well as many adjacent photoionized regions along the slits for comparison. The spectra confirm that the SNR candidates have [S II]:Hα ratios in excess of 0.4, thus satisfying the usual optical criterion for being supernova remnants. Approximately 80% of the objects observed spectroscopically show additional emission lines that support their identification as supernova remnants. These are the first large samples of supernova remnants identified in galaxies outside the Local Group. In general, many properties of these SNR samples parallel the more extensive sample identified in M33. However, the dividing line between the [S II]:Hα ratios appropriate for photoionized and shock-heated nebulae appears to be much less distinct in these galaxies than for Local Group galaxies, causing confusion and incompleteness in these samples. This confusion effect is most prevalent in NGC 7793, where the observed [S II]:Hα ratio in the most diffuse photoionized gas rises well above the value of 0.4 normally used to discriminate SNRs from H II regions.

Observations of a complete sample of H $_{\bf\alpha}$ emission-line galaxies. Long-slit spectroscopy of galaxies in UCM lists 1 and 2

Spectroscopic observations for the full sample of Her emission-line galaxy candidates (ELGs) from the Universidad Complutense de Madrid objective-prism survey Lists 1 and 2 have been obtained in order to investigate fully the properties of the survey constituents as well as the selection characteristics and completeness limits of the survey itself. The spectroscopic data include redshifts, line fluxes, equivalent widths, emission-line ratios, optical reddening estimates and synthesized color indexes. We find that 74% of the objects in this sample do exhibit emission Lines. We compare our observational data, with parameters given in the published survey lists in order to assess the usefulness of the latter. The different emission-line galaxies have been classified according to their spectra in several groups. Gray-scale images of the CCD spectra near the main emission lines, spatial profiles at the continuum and the Line for [OIII] λ5007 and Hα lines, as well as plots of the coadded spectra of selected galaxies are presented, and a number of peculiar objects are described.

THE ROSSITER-MCLAUGHLIN ROTATION EFFECT OBSERVED FOR AI DRACONIS AND V505 SAGITTARII

ABSTRACT CCD spectra were obtained for the late B and early A type Algol binaries Ai Draconis and V505 Sagittarii during their May 1991 primary eclipses. With these spectra, the Rossiter-McLaughlin rotation effect was observed. The least-squares fit to the rotation effect yielded projected rotational velocities of 85.6 ± 2.1 and 131.8 ± 2.8 km s-1 and barycentric velocities of +5.5 ± 0.4 and -0.8 ± 0.6 km s-1 for Ai Dra and V505 Sgr, respectively. Compared to their synchronous values, AI Dra appears to be rotating slightly slower while V505 Sgr is rotating considerably fastr than expected. The eclipse spectra were also examined for signs of secondary and/or tertiary companions. The third star belonging to the V505 Sgr system which was discovered by Tomkin (ApJ, 387, 631 (1992)) was easily recognized by no absorption features were found that could be directly attributed with any certainty to the secondary in either system. However, the Ca II K line in AI Dra was at times distorted and several weak, broad features were noted in V505 Sgr.

The Wolf-Rayet Star HD 197406, with Its Strongly Ionizing Close Companion

view Abstract Citations (27) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Wolf-Rayet Star HD 197406, with Its Strongly Ionizing Close Companion Marchenko, Sergey V. ; Moffat, Anthony F. J. ; Lamontagne, Robert ; Tovmassian, Gaghik H. Abstract High-quality, phase-dependent CCD spectra are presented for the first time for this unusual Population I, runaway WN7 single-line binary system. Besides confirming a previous orbit based on the N iv 4058 Å emission line, these spectroscopic data show phase-dependent, line-profile variations, especially in He II. The low mass function, but normal orbital inclination, implies that the companion is either a normal B2-B4 V-III star or a relativistic object. In either case, the phase-dependent line variations lead to the suggestion of an ionized cavity near the companion that is probably created from X-rays generated via impact of the W-R wind on the windless B star, or via accretion on the relativistic companion. This is borne out in the light curve, based on new data combined with all previously published data, which shows a broad minimum when the W-R component is closest to the observer. Compared to all other light curves known for W-R + OB systems, HD 197406's light curve requires the secondary light to arise in an extended region, presumably the hot cavity. Some preference is shown for the scenario involving a relativistic companion, from timing arguments of the orbiting ionized cavity. Despite the strong ionization, its local nature ensures that HD 197406 remains only a weak observed X-ray source. Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177067 Bibcode: 1996ApJ...461..386M Keywords: STARS: BINARIES: SPECTROSCOPIC; STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 197406; STARS: WOLF-RAYET full text sources ADS | data products SIMBAD (5)

Spectroscopy of comet P/Schaumasse

Column density profiles for CN, C3, C2 and NH have been determined from a long-slit CCD spectrum of periodic comet P/Schaumasse (1992x). Comparisons of these profiles with Haser models indicate that the ratios of the CN, C3 and C2 production rates are typical for a short-period comet. Although the scale lengths for NH and its parent species are uncertain, the results indicate that the production rate for NH is much greater than for either C2 or CN.

The UV Spectrum of the QSO OQ 172 Observed with the Faint Object Spectrograph

view Abstract Citations (7) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The UV Spectrum of the QSO OQ 172 Observed with the Faint Object Spectrograph Lyons, R. W. ; Cohen, Ross D. ; Junkkarinen, Vesa T. ; Burbidge, E. Margaret ; Beaver, E. A. Abstract Low resolution far-UV spectra of the high redshift QSO OQ 172 (Z_e_ = 3.544) have been obtained with the prism and the G160L grating of the Faint Object Spectrograph on board the Hubble Space Telescope. Light is detected down to a rest wavelength near 325 A where the spectrum appears to be cut off, possibly by a Lyman limit system. This cutoff is about 20,000 km s^-1^ longward of any predicted He II λ304 feature (the He II λ304 Gunn-Peterson effect and the He II λ304 forest). A partial Lyman limit is observed near 2826 A (z =2. 10). The UV spectra have been combined with optical CCD spectra to determine the shape of the continuum short of the Lyα emission line and model it using the "Lyman valley" equations presented by Miller & Jakobsen (A&A, 228,299(1990)]. Publication: The Astronomical Journal Pub Date: October 1995 DOI: 10.1086/117626 Bibcode: 1995AJ....110.1544L Keywords: QUASARS: INDIVIDUAL: OQ 172; QUASARS: ABSORPTION LINES full text sources ADS | data products SIMBAD (1) NED (1) MAST (1) ESA (1)

Charge‐coupled device spectra of the Galilean satellites: Molecular oxygen on Ganymede

We have obtained 3200–7800 Å CCD spectra of the Galilean satellites at a variety of orbital longitudes, with spectral resolution between 3 and 18 Å and signal‐to‐noise ratios of up to 2000 at 6000 Å. Despite the higher resolution and signal‐to‐noise ratio than previous published spectra, no new features are seen on Io, Europa, and Callisto. However, Ganymede shows an unusual and previously unreported shallow absorption feature at 5773 Å, which is much stronger on the trailing side, and a weaker band at 6275 Å. The features are apparently due to diatomic oxygen, and require simultaneous electronic transitions in two adjacent molecules: they are the strongest visible‐wavelengt h absorption bands in solid or liquid oxygen. Because condensed pure oxygen is not stable at Ganymede surface temperatures and pressures, the oxygen must be trapped in other surface materials, perhaps in water ice, with the constraint that O2 molecules must be close enough together for simultaneous electronic transitions. Magnetospheric bombardment of water ice is a plausible production mechanism for the O2. Continuum shapes on all four satellites are more clearly seen than in previous spectra. The shape of the continuum is very similar on Ganymede and Callisto but is strikingly different on Europa, indicating a different origin for the nonice component on Europa. The shape of the Europa continuum suggests that allotropes or compounds of sulfur may be the dominant spectrally active materials in the visible spectrum. No convincing changes since 1978 are visible in Io's spectrum, despite the high resurfacing rates, suggesting that volcanic resurfacing tends to overpaint areas with more material of the same composition.

Wind-Wind Interaction in the Close Wolf-Rayet Binary CQ Cephei (WN6+O9 II--Ib)

view Abstract Citations (30) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Wind-Wind Interaction in the Close Wolf-Rayet Binary CQ Cephei (WN6+O9 II--Ib) Marchenko, S. V. ; Moffat, A. F. J. ; Eenens, P. R. J. ; Hill, G. M. ; Grandchamps, A. Abstract A large collection of blue and yellow CCD spectra of the short-period eclipsing binary CQ Cep allows us to improve the double-line (SB2) orbit of Kartasheva & Snezhko and reclassify the system as WN6+O9 II-Ib. With orbital inclination i = 78° 65°, the masses and radii are Msun = 18-23 Msun, MWR = 15-19 Msun, R0 ≤ 10 Rsun, 2 Rsun ≤ RWR ≤ 10 Rsun. For its spectral type, the 0 star mass and radius are smaller than values deduced from evolutionary models but agree with recent determinations of other O stars in binaries. The W-R star is shown to contain a small amount of hydrogen in its wind. Because of the rapid orbit revolution compared to the wind velocities, the wind interaction zone is tightly wrapped around the system. We construct a phenomenological model which explains the numerous phase-dependent spectral variations. Publication: The Astrophysical Journal Pub Date: September 1995 DOI: 10.1086/176186 Bibcode: 1995ApJ...450..811M Keywords: STARS: BINARIES: ECLIPSING; STARS: EARLY-TYPE; STARS: FUNDAMENTAL PARAMETERS; STARS: WOLF-RAYET full text sources ADS | data products SIMBAD (6)

SPECTROSCOPY OF QUASAR CANDIDATES FROM THE CASE LOW-DISPERSION SURVEY

ABSTRACT We obtained CCD spectra for 24 stellar objects selected from the Case Low-Dispersion Northern Sky Survey. Fourteen are quasars which are bright enough for future absorption-line studies. Seven of these show a multitude of metallic absorption lines. The quasar redshifts range from z = 0.275 to z = 2.96 with a median of z = 2.15. Two objects are Seyfert galaxies. One object has a relatively featureless spectrum with no detected strong emission lines, and it may be a BL Lac object. Spectra of seven other objects show them to be Galactic stars.

Cooling flows, central galaxy-cluster alignments, X-ray absorption and dust

We present the analysis of pointed ROSAT Position Sensitive Proportional Counter (PSPC) observations of five of the most luminous, intermediate-redshift (0.1 <z<0.15) clusters of galaxies detected in the ROSAT All-Sky Survey. The PSPC data are combined with optical CCD images and spectra to examine the relationship between clusters and their central cluster galaxies (CCGs). Abell 1068, Abell 1361 and Abell 1664 contain three of the most optically line-luminous CCGs known. The PSPC X-ray data show that these galaxies lie at the centres of massive (200–400 M⊙ yr–1 cooling flows. The alignment between CCGs and their host clusters has been investigated. For those clusters with cooling flows, the position angles of the X-ray emission from the clusters and the optical emission from the CCGs agrees within 5°. For the one probable non-cooling flow cluster in the sample, Abell 2208, the alignment is significantly poorer. We examine the evidence for intrinsic X-ray absorption in the clusters. The X-ray spectra for Abell 1068 and Abell 1664 show that the cooling flows in these clusters are intrinsically absorbed by equivalent hydrogen column densities ≳1021 atom cm–2. The optical spectra of the CCGs in these clusters exhibit substantial intrinsic reddening, at levels consistent with the X-ray absorption results if standard dust-to-gas ratios are assumed.

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)