CCD Spectra Research Articles

CCD spectroscopy of the W Serpentis binaries KX And and RX Cas

AbstractInitial results are presented from a study of Hγ profiles in the two interacting binaries KX And and RX Cas of W Serpentis type. The used CCD spectra with a resolution of 0.13Å/px were obtained with the 2.2m telescope and the Coudé spectrograph at the German-Spanish Astronomical Center at Calar Alto/Spain.

The Bologna/ESO Search for Double Degenerates

In 1984 a program has been set up for a systematic search of double degenerates (DD) among spectroscopically confirmed white dwarfs. For each WD at least two CCD spectra are obtained, which are then cross-correlated in order to get a radial velocity difference, if any. For this purpose we have used the ESO Faint Object Spectrograph and Camera (EFOSC) attached at the ESO 3.6m telescope. Exposure times are typically in the range 5–15 min, and the typical error in the radial velocity difference (Δυx) is ∼ 20 km s−1.Until now we had two observing runs, respectively in September 1985 and January 1988, for a total of 5 usable nights. For 20 WDs we have obtained more than one spectrum. Among them we have singled out two DD candidates. The first object (WD0957–666) has shown Δυr values up to ∼ 220 km s−1 and three other spectra were kindly taken for us in April 1988 by Stefano Cristiani. These also showed Δυr,’s up to ∼ 140 km s−1. Another object (WD0954–710) exhibits a Δυr ≃ 70 km s−1. The two DD candidates will be observed again in the next observing run in order to confirm their binarity and in case determine the periods.

THE PHOTOMETRIC VARIABILITY OF THE CHROMOSPHERICALLY ACTIVE BINARY STAR HD 80715

ABSTRACT Differential UBVRI photometry of the double-lined BY Dra system HD 80715 (K3 V + K3 V) obtained in December 1987 is presented. The star is found to be a variable with a full amplitude of 0.06 mag in V and a period similar or equal to the orbital period of 3.804 days. The mechanism of the variability is interpreted as rotational modulation due to dark starspots. In an attempt to detect chromospheric activity, high-resolution CCD spectra were obtained at Ca II H and K and at Fe I 6430 A and Ca I 6439 A, the photospheric lines normally used for Doppler imaging. HD 80715 shows double H and K emission features at a constant flux level for each component.

Emission-Line Asymmetries and the Kinematics of the Narrow-Line Region in AGNs

We have obtained high signal-to-noise ratio CCD spectra at ≤ 150 km/s resolution for 6 high-ionization Seyfert galaxies. We analyzed the profiles of the emission-lines over a wide range in both ionization potential (IP) and critical density (Ncr) in order to study the fundamental problem of cloud motion in the narrow-line region (NLR). Using the known correlations between FWHM and IP and/or Ncr for these galaxies, and assuming that the blueward profile asymmetries result from the combined effects of radially infalling or outflowing clouds and extinction within or between them, we deconvolve these effects by analyzing the correlation between emission-line asymmetries and both IP and Ncr. We find fair to good correlations in the sense that lines with high IP and Ncr also tend to have high asymmetry, while lines with low IP and Ncr have low but usually non-zero asymmetry. Simulated emission-line profiles generated with a spherically-symmetric model of a NLR suggest that the extinction arises primarily within radially infalling clouds.

Oxygen abundances in old disc and halo stars of the Galaxy

Intermediate resolution (λ/δλ ∼ 25 000) CCD spectra of the oxygen triplet at λ7770 A have been analyzed to determine oxygen abundances in a sample of metal-deficient stars with metallicities covering the range −2.5≤[Fe/H]≤−0.2. Important oxygen overabundances ([O/Fe]≥1) are found in the more metal deficient stars of the sample. We briefly discuss the information that these observations provide about the early nucleosynthesis history and chemical evolution of the Galaxy.

Spatially resolved spectroscopy of the gravitational lens system 2237 + 030

Long-slit CCD spectra of the central region of the gravitational-lens system candidate 2237 + 030 were obtained at the CFHT. The slit was placed in two position angles covering two of the four quasar component candidates at a time. The brightest two components (A and B) are spatially resolved and have similar emission-line profiles in the semiforbidden line of C III. The fainter two components (C and D) are marginally resolved spatially, and have C III profiles similar to those observed for components A and B, although there is substantial contamination through scattering from A and B. The spatial position and extent of the C III emission line from the spectrum of components C and D are found to be consistent with the hypothesis that at least component C has a quasar spectrum identical to that of components A and B. The spectroscopic data strongly confirm the hypothesis that 2237 + 030 is a gravitational-lens system. 11 references.

The electron temperature and optical emission structure of the central component of CTB 80

Optical spectra on the central component of the galactic supernova remnant CTB 80 are presented. Long slit CCD spectra reveal relative line-intensity variations among individual filaments, the presence of Balmer-dominated emission in the core's east and west optical lobes, and no radial velocities in excess of 300 km/s. Aperture spectrophotometry of the temperature-sensitive forbiddden O III lines suggests Te = 25,000 K, thus favoring a shock-heated interpretation for the remnant's optical core emission. These results indicate that fundamental differences exist betweem the optical emission of CTB 80's central core component and the Crab Nebula, despite similarities in these remnants' radio and X-ray properties. The optical emission from CTB 80's core is likely to be a direct result of the interaction of an active pulsar with its adjacent partially neutral interstellar medium. The size of CTB 80's outer structure and the absence of either high velocity or enhanced abundances in the region local to CTB 80's pulsar argue for a considerably larger age for CTB 80 than the Crab Nebula's 1000 yr. A qualitative picture for CTB 80 that can plausibly explain many of the core's properties is proposed.

OBSERVATIONS OF GLIESE 890 AND OTHER POSSIBLY RAPIDLY ROTATING FIELD M DWARFS

ABSTRACT BV photometry of the rapidly-rotating M dwarf Gliese 890 (dM2e) obtained in 1983-84 is presented. The long-term photometric behavior of the star is examined, and evidence is found for the presence of persistent polar active regions, as has been proposed by Young at al. (1987). In an attempt to detect additional rapidly-rotating field M dwarfs similar to Gliese 890, four dM stars suspected by Cowley and Hartwick (1982) to show broadened absorption lines are observed. CCD spectra with 1-A resolution fail to show any evidence for line broadening. The H-alpha line is in absorption in all four stars.

Non-LTE Effects and Abundance Analyses of Halo Stars

The possible existence of departures from LTE affecting the abundance analyses of halo dwarfs and subgiants is analysed from the observational point of view, and illustrated by the case of the intermediate halo subgiant HD 76932. High resolution and high S/N Reticon and CCD spectra have been obtained with the ESO Coude Echelle Spectrometer. A detailed model atmosphere analysis has been carried out, which reveals a number of inconsistencies. In particular, the iron abundance derived from the neutral lines shows a very clear excitation potential dependence. Similar effects appear for oxygen and calcium and, possibly, for magnesium, chromium and ionized iron. Some overionization also seems to be present in a number of elements. The impact of these effects on the derived abundances may be rather large (some 0.2 to 0.6 dex). In particular, doubts might be raised about the reality of the oxygen overabundance and the odd-even effect in Na, Mg and Al.

Oxygen in Halo Giants

High resolution CCD spectra were obtained in the region λλ6290-6330 A containing the |OI| λ6300.3 A line for a sample of halo giants. Synthetic spectra were computed to derive their oxygen abundances. A mean value [O/Fe] ≃+0.35 is obtained.

A SPECTROSCOPIC STUDY OF THE OPEN CLUSTER NGC 2281.

ABSTRACT Photographic spectra of 16 stars in NGC 2281 (= C0645+411) have been used to derive a mean E(B-V) = 0.11 mag and a true distance modulus of 8.3, in agreement with earlier studies. Radial velocities of most of the same stars were derived from low-resolution CCD spectra to yield a mean cluster velocity of +5 km/s. Rotational velocities estimated from low-dispersion photographic spectra yield a distribution of the mean v sin i's as a function of absolute magnitude typical of intermediate-age open clusters. The latter result suggests that stellar evolutionary effects largely eliminate differences in the cluster mean rotational velocity distributions by the time clusters are between 50-100 x 10 to the 6th years old.

CCD observations of diffuse interstellar bands in reflection nebulae

view Abstract Citations (97) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CCD Observations of Diffuse Interstellar Bands in Reflection Nebulae Josafatsson, Karl ; Snow, Theodore P. Abstract CCD spectra of 59 stars have been obtained in order to measure diffuse band strengths between 5690 and 5870 A. Most (37) off the stars are in reflection nebulae, and the rest are relatively unreddened comparison stars. The pixel spacing corresponds to 0.2 A, and the signal-to-noise (S/N) ratio ranges from 60 up to 600. Six diffuse bands are measurable in the data: 5705, 5778, 5780, 5797, 5844, and 5849 A. Based on the degree of correlation between the bands in pairs, as well as with E(B-V) and the 2175 A extinction bump, the bands can be divided into three groups. The first one consists of the narrow bands at 5780, 5797, and 5849 A. The second group contains the broad bands at 5778 and 5844 A, while 5705 A lies in between these groups in terms of correlation behavior. The second group correlates very badly with E(B-V), and the very broad 5778 A band is the only one that shows a very good correlation with the 2175 A bump. Publication: The Astrophysical Journal Pub Date: August 1987 DOI: 10.1086/165468 Bibcode: 1987ApJ...319..436J Keywords: Charge Coupled Devices; Diffuse Radiation; Interstellar Matter; Reflection Nebulae; Spectral Bands; Stellar Spectra; Molecular Clouds; Signal To Noise Ratios; Astrophysics; INTERSTELLAR: MATTER; INTERSTELLAR: MOLECULES; NEBULAE: REFLECTION full text sources ADS | data products SIMBAD (60)

Fine-scale motion in NGC 6514 and NGC 6523

Velocity maps of the inner regions of the bright H II regions NGC 6514 and NGC 6523 were made with unprecedented spatial and spectral resolution in the 5007 A line of forbidden O III. In addition to the advantages of an instrumental full width at half-maximum intensity of only 5.4 km/s, the small thermal width of the heavy oxygen ion also allows determination of accurate line widths and velocities. The CCD spectra were numerically fitted to Gaussian line profiles and revealed two separate velocity systems in NGC 6523. The data sets of radial velocities were used to derive the dependence of the most probable turbulent velocities upon the sample sizes, and the spatial dependence of the structure function. These relationships are the basic functions for comparison with the predictions of the models for turbulence in H II regions.

High-resolution CCD spectra of stars in globular clusters. III - M4, M13, and M22

Spectra of 0.3 and 0.6 A resolution of stars in M4, M13 and M22 to derive abundances of various atomic species and the CN molecule. For M13, the usual Fe/H ratio and a surprisingly high aluminum abundance is found. The CN lines indicate a larger column density in the oxygen-rich star III-63 than in the oxygen-poor star II-67 by a factor of 10. It appears that II-67 is deficient in C, N, and O by about a factor 3 relative to iron for all three elements. For M4, Fe/H = -1.2 using solar f values derived via the Bell et al. (1976) model. This Fe abundance lies between earlier echelle values and photometric values. For two stars, CN data are obtained that can be understood if there was a slight excess of C/Fe and N/Fe prior to CN cycling and mixing. For M22, a large difference in CN is found between stars III-3 and IV-102. The origin of the CNO elements is discussed in terms of mass loss from an early generation of red giants and possibly Wolf-Rayet stars.

THE RING-SHAPED NEBULAE AROUND FU ORIONIS STARS.(HARO 2-249 = HARO 4-249).

ABSTRACT All five of the known FU Orionis stars are associated with ring-shaped nebulae. Deep CCD images and spectra are presented of three of the nebulae, those associated with V1057 Cyg, V1515 Cyg, and V1735 Cyg. The spectra of all three nebulae are clearly from reflection. A crude model for the dust shells is briefly discussed, and it is argued that the shells may indicate a relatively advanced evolutionary state for the FU Orionis stars. The elongated shape of the shells may be the result of the relative motion of the star through the parent molecular cloud, in which case there is only a single cavity. The FU Orionis outburst itself may then occur when the star reaches the edge of the cavity and fresh material is accreted. Some of the more recent models for the outburst itself are discussed and some observational tests of these models suggested.

High-resolution CCD spectra of stars in globular clusters. II - Metals and CNO in M71

Palomar coude CCD spectra of resolution 0.3 and 0.6 has been used to redetermine abundances in five stars of the relatively metal rich globular cluster M71. The (Fe/H) value is restricted to the limits of -0.6 to -1.0. The largest source of uncertainty is a systematic difference in f-values between those derived via the Holweger-Muller (1974) solar model and the Bell et al. (1976) solar model. If we use absolute f-values measured by the Oxford group (Blackwell et al. 1982) we find Fe/H to lie in the range of -0.6 to -0.75, i.e., as given by using the Bell et al. solar model. The relative abundances of the light elements, i.e., Na through Ca and probably including Ti show an average excess relative to iron of 0.4 dex. The effect of this difference on metal indices derived from broad- and narrow- band photometry is discussed. For three stars we find O/H = -0.6 using absolute f-values. For CN an analysis of individual rotational lines of the 2-0 band of the red system yields lines in the (C/H,N/H) plane that are consistent with either an original C/Fe = N/Fe = 0 or a modest increase in N relative to C due to CN burning and mixing. A search for C-13N was not successful and an uncertain lower limit of C-12/C-13 near 10 was obtained.

AN OPTIMAL EXTRACTION ALGORITHM FOR CCD SPECTROSCOPY.

ABSTRACT An optimal spectrum extraction procedure is described, and examples of its performance with CCD data are presented. The algorithm delivers the maximum possible signal-to-noise ratio while preserving spectrophotometric accuracy. The effects of moderate geometric distortion and of cosmic-ray hits on the spectrum are automatically accounted for. In tests with background-noise limited CCD spectra, optimal extraction offers a 70-percent gain in effective exposure time in comparison with conventional extraction procedures.

High-resolution CCD spectra of stars in globular clusters. I - Oxygen in M13

High-resolution (0.3 A) CCD spectra obtained at the 200 in. coude spectrograph have been analyzed for the abundances of O, Sc, Fe, and La in four stars in the globular cluster M13. Fe/H abundance is found to be = -1.6, as found by many other observers of this cluster. For three stars O/Fe abundance is found to be = +0.3 + or - 0.1, which is similar to O/Fe ratios in other globular clusters and metal-poor field stars. For star II-67, no oxygen line is visible at 6300 A and O/Fe abundance is found to be not greater than -0.4 (for a high carbon content) and not greater than -0.7 (for a low carbon content). The latter is more likely to be correct. Two possible explanations of the oxygen deficiency in II-67 are discussed: primordial deficiency, and CNO cycling at or above a temperature of 25,000,000 K.

CCD observations of comet Tuttle 1980 XIII - The H2O(+) ionosphere

A CCD spectrum of comet Tuttle 1980h has been analyzed with emphasis on the emission of H2O(+) ions. The fine angular resolution (1.5 arcsec) and the capability of absolute brightness calibration of the CCD instrument made it possible to determine the spatial concentration of the H2O(+) ions of this faint comet and the total number of these ions confined within a spherical region. Solar photoionization of the H2O atmosphere can account for the production of the H2O(+) ions observed in the confined region. The dimension of the H2O(+) ionosphere at the time of observation was found to be comparatively small, implying the possible existence of an ionopause sharply delineating the extension of the cometary ionosphere.

A Study of the Short-Period Cepheid EU Tauri

EU Tauri is a classical Cepheid with one of the shortest period known. A Fourier decomposition study of its V light curve by Simon S Lee (1981) revealed a peculiar position in phase-period diagrams, very similar to the star SU Cas which is probably an overtone pulsator (Gieren, 1982). This suggested the possibility that EU Tau might be another galactic overtone pulsator. In order to investigate this question, some 100 new photometric observations of this star on the UBVRI (Johnson) system were obtained with the #2 0.9m telescope of KPNO. Simultaneously, 43 CCD spectra of the star were secured on the Coudé feed telescope of KPNO which were measured for radial velocities using a correlation technique. These velocities have an internal accuracy of better than 0.5 km/s and define a complete velocity curve of EU Tau.