CCD Spectra Research Articles

Spectroscopic investigations of classical Cepheids and main-sequence stars in galactic open clusters and associations

The small-amplitude Cepheid V1726 Cyg and two members of open cluster Platais 1 (Platais 1 star No. 1 (1921) and Platais 1 star No. 111 (1600)) were investigated, using high-resolution CCD spectra. The following results were obtained: 1) All objects have the same metallicities, close to that of the Sun (for V1726 Cyg weighted average [ Fe/H$]=+0.05$, for Platais 1 star No. 1 (1921) [ Fe/H$]=+0.13$); 2) values of T eff and $\log g$ for the B-stars are in excellent agreement with those determined from $(B-V)$ colour indices using a $(B-V)\sim(T_{\rm eff}$, $\log g$) calibration; 3) the elemental abundances indicate that V1726 Cyg is in the post first dredge-up stage with an age near $1.5 \times 10^{8}$, and is crossing the Cepheid instability strip for the third time. Mean values of $T_{\rm eff}=6100$ K and $\log g=2.35 \pm 0.05$ permit us to refine its colour excess to $E_{B-V}=0\fm 33$, which for a distance of $d = 1568\pm 13$ pc corresponds to $M_{V}=-2\fm 99$. The Cepheid could therefore be pulsating in the fundamental tone, although pulsation in the first overtone is not excluded; 4) Platais 1 star No. 1 (1921) is a slowly rotating HgMn-star with a high helium content, while Platais 1 star No. 111 (1600) is a rapidly rotating main-sequence star with a helium content comparable to that of the Sun; 5) the age of the open cluster is estimated to be about $2.5 \times 10^{8}$ yr.

The Spectrum of VY Canis Majoris in 2000 February

ABSTRACTWe present the current (2000 February) status of the optical spectrum of the irregularly variable M supergiant VY CMa, based on high‐resolution CCD spectra. The emission spectrum is largely unchanged over the past 43 yr, with low‐lying atomic lines as well as the molecules TiO and ScO in emission. Tables of observed wavelengths for both identified and unidentified lines are presented.

Optical spectra of three AGB stars

The basic parameters and detailed chemical compositions of three asymptotic giant branch stars with similar effective temperatures and surface gravities have been determined using CCD spectra obtained with the echelle spectrometers of the SAO 6-m telescope. The metallicity and chemical composition of the optical counterpart of the OH/IR star IRAS 18123 + 0511 have been derived for the first time. The abundance [X/H]⊙ of the iron group elements (V, Cr, Fe) is −0.45 dex. An overabundance of oxygen, [O/Fe]⊙=1.44 dex, is detected in the atmosphere of this star. The abundances of s-process heavy elements are not enhanced, and are instead underabundant with respect to the metallicity: the average value of [X/Fe]⊙ for Y, Zr, Ba, La, Ce, Pr, Nd is −0.25. The derived abundances confirm that IRAS 18123 + 0511 is in the AGB stage of its evolution. The metallicity of the object, together with its radial velocity V r=78.0 km/s and Galactic latitude |b|=11°, suggest that it belongs to the old disk population. The expansion velocity of the circumstellar envelope, V exp≈21 km/s, is derived from the positions of circumstellar absorption bands. The set of parameters obtained for the low-metallicity, highlatitude supergiants BD + 18° 2757 and BD + 18° 2890 (with iron abundances [Fe/H]⊙=2.10 and −1.48, respectively) confirm that they are evolved halo stars, and probably UU Her-type stars.

LB 8827: A Variable, Magnetic DBA White Dwarf

We present accurate CCD spectropolarimetry and spectra that show that the hot DB star LB 8827 (PG 0853+164) is a weakly magnetic, variable DBA white dwarf. We confirm Putney's detection of circular dichroism in the He I lines, but on three occasions we measure a weaker field strength and opposite sign of circular polarization, Be 100 kG. The Balmer line strengths appear to vary with time, indicative of changes in the apparent H/He abundance ratio or irregularities over the stellar surface. Fits to the observed energy distribution and to the optical He I line spectrum with model atmospheres yield effective temperatures in the 21,200-27,700 K range, with lower values favored. This suggests that LB 8827 falls within or near the instability strip of the V777 Herculis stars. High time resolution photometric observations presented here rule out white-light brightness variations with amplitudes larger than 1.2 mmag in the period window 20 s to 2 hr. The possibility that the magnetic field might tend to suppress pulsations is discussed.

ChandraObservations of Variable Embedded X‐Ray Sources in Orion. I. Resolving the Orion Trapezium

We used the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory to perform two observations, separated by 3 weeks, of the Orion Trapezium region. The zeroth-order images on the Advanced CCD Imaging Spectrometer provide spatial resolution of 05 and moderate energy resolution. Within a 160'' × 140'' region around the Orion Trapezium, we resolve 111 X-ray sources with luminosities between 7 × 1028 and 2 × 1032 ergs s-1. We do not detect any diffuse emission. All but six sources are identified. From spectral fits of the three brightest stars in the Trapezium, we determine the line-of-sight column density to be NH = (1.93 ± 0.29) × 1021 cm-2. Many sources appear much more heavily absorbed, with NH in the range of 1022-1023 cm-2. A large fraction of sources also show excursions in luminosity by more than a factor 5 on timescales greater than 50 ks; many are detected only in one of the observations. The main objective of this paper is to study the Orion Trapezium and its close vicinity. All five Trapezium stars are bright in X-rays, with θ1 Ori C accounting for about 60% of the total luminosity of the Trapezium. The CCD spectra of the three very early-type members can be fitted with a two-temperature thermal spectrum with a soft component of kT ~ 0.8 keV and a hard component of kT ~ 2-3 keV. θ1 Ori B is an order of magnitude fainter than θ1 Ori E and shows only a hard spectrum of kT ~ 3 keV. θ1 Ori D is another order of magnitude fainter than θ1 Ori B, with only a kT ~ 0.7 keV component. We discuss these results in the context of stellar wind models. We detect eight additional, mostly variable X-ray sources in the close vicinity of the Trapezium. They are identified with thermal and nonthermal radio sources, as well as infrared and optical stars. Five of these X-ray sources are identified with proplyds, and we argue that the X-ray emission originates from class I, II, and III protostars at the cores of the proplyds.

Spectroscopic investigations of classical Cepheids and main-sequence stars in galactic open clusters and associations

The small-amplitude Cepheid SU Cas and four members of the association Cas OB2 (HD 16893, HD 17327a and b, HD 17443) were investigated, using high-resolution CCD spectra. The following results were obtained: 1) All these objects have the same metallicity values, close to that of the Sun; 2) Elemental abundance indicates that SU Cas is a post first dredge-up star with an age from 1 10 to 1.45 10 yr, and it is not crossing the Cepheid instability strip for the first time. The mean value of log g = 2.35 corresponds to pulsations in the fundamental tone, although errors in gravity estimations provide overtone pulsations. The questions about its pulsational mode and membership in Cas OB2 remained open; 3) HD 17327a is a slowly rotating HgMn–star with the highest helium content among such objects, while HD 16893 also has a manganese overabundance and might be classified as an Am–star; 4) HD 17327b and HD 17443 are rapidly rotating main-sequence stars, while HD 17443 has a helium content comparable with that of the Sun.

High-resolution X-ray spectroscopy and imaging of supernova remnant N132D

The observation of the supernova remnant N132D by the scientific instruments on board the XMM-Newton satellite is presented. The X-rays from N132D are dispersed into a detailed line-rich spectrum using the Reflection Grating Spectrometers. Spectral lines of C, N, O, Ne, Mg, Si, S, and Fe are identified. Images of the remnant, in narrow wavelength bands, produced by the European Photon Imaging Cameras reveal a complex spatial structure of the ionic distribution. While K - shell Fe seems to originate near the centre, all of the other ions are observed along the shell. An emission excess of O(6+) over O(7+) is detected on the northeastern edge of the remnant. This can be a sign of hot ionising conditions, or it can reflect a relatively cool region. Spectral fitting of the CCD spectrum suggests high temperatures in this region, but a detailed analysis of the atomic processes involved in producing the O(6+) spectral lines leads to the conclusion that the intensities of these lines alone cannot provide a conclusive distinction between the two scenarios.

Electron Heating and Cosmic Rays at a Supernova Shock from [ITAL]Chandra[/ITAL] X-Ray Observations of 1E 0102.2−7219

In this Letter, we use the unprecedented spatial resolution of the Chandra X-Ray Observatory to carry out, for the first time, a measurement of the postshock electron temperature and proper motion of a young supernova remnant, specifically to address questions about the postshock partition of energy among electrons, ions, and cosmic rays. The expansion rate, 0.100% ± 0.025% yr-1, and inferred age, ~1000 yr, of 1E 0102.2-7219, from a comparison of X-ray observations spanning 20 yr, are fully consistent with previous estimates based on studies of high-velocity oxygen-rich optical filaments in the remnant. With a radius of 6.4 pc for the blast wave estimated from the Chandra image, our expansion rate implies a blast-wave velocity of ~6000 km s-1 and a range of electron temperatures 2.5-45 keV, dependent on the degree of collisionless electron heating. Analysis of the Chandra CCD spectrum of the immediate postshock region reveals a thermal plasma with abundances and column density typical of the Small Magellanic Cloud and an electron temperature of 0.4-1 keV. The measured electron temperature is significantly lower than the plausible range above, which can be reconciled only if we assume that a significant fraction of the shock energy, rather than contributing to the heating of the postshock electrons and ions, has gone into generating cosmic rays.

H α and Ca II triplet spectroscopy of cataclysmic variables and related objects

In this paper, some CCD spectra of 6 cataclysmic variables: AB Boo, T CrB, UX UMa, AH Her, Z Cam, V426 Oph and 3 related objects: Leo3, UMa3 and EG UMa are presented. We also observed 5 late-type stars: 3 Dra, ν Vir, ψ Leo, 34 Boo, and 36 Com in order to provide comparison with the late-type component of the program systems. The observations were made using the 2.16 m telescope of Bejing Observatory with a Cassergrain spectrograph on 1997-04-15/17 at the Xinglong Station. The CCD spectra were obtained with a low resolution and a dispersion of 1.2Å/pixel. The spectral region covered is from 5920Å to 7072Å, and from 7950Å to 9180Å for all the program stars and only 3390–8380Å for AH Her. Representative spectra are given for each object. The equivalent width (EW) and FWHM of H αand CaII triplet lines were determined. The radial velocities for 9 program stars were also determined. Implications of our results are discussed.

Optical spectrum of the infrared source IRAS 23304+6147

Based on CCD spectra obtained with the PFES echelle spectrometer of the 6-m telescope, we have determined for the first time the effective temperature T eff=5900 K, surface gravity logg=0.0, and detailed chemical composition of the faint star identified with the infrared source IRAS 23304+6147 by the model-atmosphere method. Its metallicity indicates that the object belongs to the old Galactic disk (the mean abundance of the iron-group elements V, Cr, and Fe for IRAS 23304+6147 is [X/H]=−0.61 dex). The stellar atmosphere exhibits an enhancement of carbon and nitrogen, [C/Fe]=+0.98, [N/Fe]=+1.36, and C/O>1. Significant overabundances of lanthanides were detected: the mean [X/Fe]=+1.04 for La, Ce, Pr, Nd, and Eu. The elemental abundances suggest that the atmospheric chemical composition of IRAS 23304+6147 was modified mainly by nucleosynthesis followed by mixing. By modeling the object's spectrum, we revealed absorption features at the positions of well-known absorption diffuse interstellar bands (DIBs). An analysis of radial-velocity and intensity measurements for these DIBs leads us to conclude that, for IRAS 23304+6147, the DIBs originate mostly in its circumstellar dust envelope expanding at a velocity of about 20 km s−1. Molecular C2 Swan emission bands were detected in the object's spectrum, which also originate in the circumstellar envelope. There is a close match between the object's atmospheric effective temperatures determined independently by the model-atmosphere method and by modeling its optical and infrared energy distribution, within the accuracy of the methods.

Spectroscopic Investigations of the Main-Sequence B Stars in the Association Cas OB2 and the Open Cluster Platais 1 (C2128+488)

AbstractA spectroscopic investigation of four main-sequence stars in the association Cas OB2 (HD 17327A and B, HD 16893, HD 17443) and of two stars in the open cluster Platais 1 (No. 1 (1921) and No. 111 (1600)) was carried out using high-resolution CCD spectra, obtained with echelle-spectrometer ”LYNX” (6-m telescope, Special Astrophysical Observatory, Russian Academy of Sciences). We have determined the atmospheric parameters for the program stars, their projected rotational velocities and elemental abundances in their atmospheres. Two new HgMn stars - HD 17327A and Platais No. 1 - were detected. HD 17443 is not a Be star.

Spectrophotometry: Revised Standards and Techniques

ABSTRACTThe telluric features redward of 6700 Å have been removed from the accurate spectrophotometric standards of Hamuy et al. to permit more reliable relative and absolute spectrophotometry to be obtained from CCD spectra. Smooth fluxes from 3300 to 10500 Å are best determined by dividing the raw spectra of all objects taken in a night by the raw spectrum of a “smooth” spectrum star before deriving the instrumental response function using the revised standard star fluxes. In this way the telluric features and any large instrumental variation with wavelength are removed from the raw data, leaving smooth spectra that need only small corrections to place them on an absolute flux scale. These small corrections with wavelength are well described by a low‐order polynomial and result in very smooth flux‐calibrated spectra.

CCD spectra of MK standards and a preliminary extension of the MK classification to the yellow-red region: SHI Huo-ming & HU Jing-yao Shanghai Observatory, CAS, Shanghai 200030

CCD spectra of MK standards and a preliminary extension of the MK classification to the yellow-red region: SHI Huo-ming & HU Jing-yao Shanghai Observatory, CAS, Shanghai 200030

Shallow water bathymetry using integrated airborne multi-spectral remote sensing

An integrated low cost airborne multi-spectral remote sensing system is described and evaluated for remote sensing for shallow water bathymetry. The system consists of: two 35mm motor driven reconnaissance cameras using colour and colour infrared film. Three optically filtered (including removable internal IR cut-off filters), electronically shuttered CCD progressive scan cameras (Sony XC-7500) integrated into an airborne direct digital recording system using a PC processor, a 32-bit RGB analogue to digital conversion card and Zip disk storage. Two CCD based imaging spectrometers providing approximately 10nm bandwidth spectral data across the CCD spectrum (400nm to 1000nm). These CCD cameras were used with a variable interference filter fixed in front of the sensor surface. This provided a 'rainbow' image of the ground varying across the image from 400nm to 700nm (visible) and 700nm to 1000nm. Field studies were undertaken to evaluate the performance of digital multi-spectral (DMV) imagery, supplementary reconnaissance photography (SRP) and VIFIS imaging spectrometry for mapping shallow water bathymetry. The results indicate good performance in shallow water and suggest that with further refinement the system could be used to give a quick comprehensive estimate of shallow water depths

Photometry and spectroscopy of the central star of the Trifid nebula

UBV photometry of the central star of the Trid nebula - HD 164492, which has so far been sus- pected of photometric as well as of radial velocity vari- ability - is presented. The results of our photometry do not conrm any variability. Moreover, based on new high resolution CCD spectra any radial velocity variability can be discarded. Photometry of several other members of the multiple stellar system is included; according to this pho- tometry, the system is a physical one. Equivalent widths for the main component of HD 164492 are given. Positions measured on CCD exposures are presented too.

CCD images and long-slit spectroscopy of the ring nebula around Mus

We present the first digital CCD images and long-slit spectroscopy of the optical ring nebula around the Wolf–Rayet star v Mus. The CCD images obtained through narrow-band filters centred at [O iii] and Ha show that the nebula has a filamentary structure, similar to supernova remnants, mainly seen in [O iii]. A spatial detachment between [O iii] and Ha images suggests excitation stratification, or multiple rings. An analysis of the physical conditions in the nebula was performed by means of long-slit CCD spectra. The spectral images show that the nebula is of low density and medium excitation. By means of quotients of recombination and collisional spectral line fluxes we determine that the principal excitation mechanism is photoionization. We have determined the electronic temperature and density, and chemical abundances for the oxygen at different sites within the nebula. Nebular chemical abundances are found to be similar to the Galactic ISM, indicating that the nebula is mainly composed of swept up material.

The distances to the X-ray binaries LSI +61° 303 and A0535+262

Chevalier & Ilovaisky (1998) use Hipparcos data to show that the X-ray binary systems LSI+61 303 and A0535+262 are a factor of ten closer (i.e. d = few hundred pc) than previously thought (d = 2 kpc). We present high quality CCD spectra of the systems, and conclude that the spectral types, reddening and absolute magnitudes of these objects are strongly inconsistent with the closer distances. We propose that the Hipparcos distances to these two systems are incorrect due to their relatively faint optical magnitudes.

Concerning the Reported Phase‐modulated Changes in the Spectrum of 41 Sextantis

ABSTRACTSreedhar Rao et al. have reported that the metallic‐line star 41 Sextantis exhibits significant changes in the depths and equivalent widths of its spectral lines and that these changes are coupled with the orbital motion of this spectroscopic binary. Based on their discovery, they suggest that 41 Sex is a possible evolutionary link between the Am and Ap stars. High‐dispersion CCD spectra of 41 Sex, obtained in 1991 with the 0.9 m feed telescope and coudé spectrograph at the Kitt Peak National Observatory, were measured to determine the equivalent widths and depths of several metallic lines and the depths of Ca ii K and H8 as a function of orbital phase. The spectrum changes that Sreedhar Rao et al. observed could not be verified with these data. Possible explanations for this lack of confirmation might be that the star was in a quiescent state in 1991 or that the reported changes to the spectrum happen on a timescale much greater than the orbital period. An updated solution for the spectroscopic orbital elements is also presented.

Separate Spectra of the Components of the Low‐Mass BinariesRoss 614A,B and L722−22A,B

ABSTRACTThe Hubble Space Telescope Faint Object Spectrograph has been used to acquire separate spectra of each of the component stars in the binaries Ross 614A,B (Gl 234A,B) and L722−22A,B (GJ 1005). Spectral types have been determined for each: M4.0 V, M5.5 V, M3.5 V, and M5.0 V, respectively, relative to a series of ground‐based CCD spectra, in the 6500–8000 Å region. The four members of the two binaries form a narrow locus in the spectral type–mass plane, from 0.18 to 0.08 M⊙ and reaching 0.08 M⊙ near spectral type M6.0. Both binaries are believed to be members of a relatively young disk population. Their masses and newly determined spectra imply that the apparently single M dwarf stars, of a similar population and with spectral types of M6, are likely to be near, or less massive than, 0.08 M⊙. Presumably, dwarf M7, M8, and M9 stars of a similar age and population are in a declining mass sequence and thus should reach well below the theoretical main‐sequence mass limit of 0.08 M⊙ and by current theory are substellar or “brown dwarf” objects.

Lithium and metal abundances in long period Am binaries

High signal-to-noise CCD spectra of three bright, long period Am binaries (HD 108651, HD 116657 and HD 138213) have been obtained and the atmospheric abundances of identied chemical elements were studied. We found HD 116657 to be a new candidate as a Li de- cient, long period Am binary, in addition to 16 Ori. While HD 108651 and HD 116657 have pronounced Am charac- teristics, HD 138213 is just a mild Am star. These stars were further studied in a more general con- text related to the role of binarity in CP phenomenon. It was found that both Li abundance and the equivalent with ratio Ca I 6718/Fe I 6679 are more peculiar in systems with more pronounced eccentricities. Such behaviour is the op- posite of what was previously found in Ap binaries and their anomalies. It indicates that tidal eects are of cru- cial importance in driving CP phenomena.