The New `High Resolution Spectral Atlas of Telluric Lines'

It is suggested that the purposes for which the atlas of telluric lines was recently published in this journal are better served by previous works of higher quality. This revised version was published online in July 2006 with corrections to the Cover Date.     

Measurements of the Stellar Velocity Dispersions of Seyfert Galaxies

The close relation between the mass of the central black hole of galaxy and the stellar velocity dispersion of bulge indicates that it is of especial importance to accurately measure the stellar velocity dispersion for determining the mass of the central black hole of galaxy. A method which uses the spectra of SDSS (Sloan Digital Sky Survey) to measure the velocity dispersion and its uncertainty is provided in this paper. Through fitting four different spectral regions which contain remarkable characteristic absorption lines in pixel space, the spectral regions used to accurately measure the stellar velocity dispersion σ are obtained. In this paper, the absorption lines which are mainly contained in these four fitted bands are Ca II K, Mg I b triplet (with wavelengths of 5 167.5, 5 172.7, 5 183.6 Å) and CaT (Ca II triplet with wavelengths of 8 498.0, 8 542.1, 8 662.1 Å). As indicated by the results in different regions, the values of σ obtained by fitting the Mg I b region are small because this region is affected by the emission lines of iron group; the spectral line in the Ca II K line region is easily restricted to the searching algorithm of least square method because its strength is very weak; the stellar velocity dispersions obtained in the combined region of CaT and Ca II K are equivalent to the results given by calculating only the CaT region. This method is used to test a sample of Seyfert galaxies whose redshifts are less than 0.05. It is found that the CaT region is the best spectral region for measuring the stellar velocity dispersion.     

Plasma laser star model of QSOs

Varshni maintained that the emission lines observed in QSOs can be satisfactorily explained as being due to laser action in certain atomic species in the expanding envelope of a star and having no appreciable redshift. In order to test this hypothesis we have examined the conditions conducive to laser action in the stellar atmosphere and compared all the emission lines of 633 QSOs discovered till August 1976 (as listed by Burbidgeet al.) with the laser transitions found in the laboratory till April 1976 (as listed by Willett and Becket al.). It was found that 88% of the QSO lines agreed to within 10 Å with the laser lines and 94% agreed to within 20 Å. The main reason Greenstein and Schmidt failed to fit the spectral lines of 3C 48 and 3C 273 with known emission lines is that laser transitions in hydrogen do not occur in stellar atmospheres. The spectra are explained on the basis of the new theory and the broadening of lines explained.     

On the accuracy of line-of-sight velocity measurements using telluric lines as reference lines

It is demonstrated that telluric lines H₂O and O₂ are displaced as much as 0.2 mÅ as the solar disk is being scanned. The temporal variations of such displacements have a quasi-periodic character.     

Contamination of the 5394 Å spectral region by telluric lines

The spectral region in the vicinity of 5394 Å contains three prominent photospheric spectral lines, which can be used as a solar plasma diagnostic tool. The occurrence of telluric lines in this region is a potential source of systematic and random errors in these solar spectral lines. The goal of our investigation was to determine the telluric line contamination of this interesting spectral region. Several series of high-resolution solar spectra within an interval of about 4 Å around the 5394 Å wavelength were observed at different zenith distances of the Sun. Comparison of these spectra has permitted identification of telluric lines in this spectral interval. The observations were carried out with the horizontal solar spectrograph of the Heliophysical Observatory in Debrecen. Telluric feature blending was identified in the blue and red wings of the Fe I 5393.2 Å line, and in the local continuum of the Mn I 5394.7 Å line. The blue wing of the Fe I 5395.2 Å line is contaminated by a weak telluric feature too. The red continuum of this line has a more prominent telluric contamination. A dozen of water vapor telluric lines that determined the observed telluric features were identified in this spectral interval. The profiles of three telluric lines that have a significant influence on both the profiles of solar spectral lines and the level of local continuum were derived, and the variation of their parameters (equivalent width and central depth) with air mass were analyzed.     

High precision radial velocities with GIANO spectra

Radial velocities (RV) measured from near-infrared (NIR) spectra are a potentially excellent tool to search for extrasolar planets around cool or active stars. High resolution infrared (IR) spectrographs now available are reaching the high precision of visible instruments, with a constant improvement over time. GIANO is an infrared echelle spectrograph at the Telescopio Nazionale Galileo (TNG) and it is a powerful tool to provide high resolution spectra for accurate RV measurements of exoplanets and for chemical and dynamical studies of stellar or extragalactic objects. No other high spectral resolution IR instrument has GIANO’s capability to cover the entire NIR wavelength range (0.95-2.45 μm) in a single exposure. In this paper we describe the ensemble of procedures that we have developed to measure high precision RVs on GIANO spectra acquired during the Science Verification (SV) run, using the telluric lines as wavelength reference. We used the Cross Correlation Function (CCF) method to determine the velocity for both the star and the telluric lines. For this purpose, we constructed two suitable digital masks that include about 2000 stellar lines, and a similar number of telluric lines. The method is applied to various targets with different spectral type, from K2V to M8 stars. We reached different precisions mainly depending on the H-magnitudes: for H ～ 5 we obtain an rms scatter of ～ 10 m s^?1, while for H ～ 9 the standard deviation increases to ～ 50 ÷ 80 m s^?1. The corresponding theoretical error expectations are ～ 4 m s^?1 and 30 m s^?1, respectively. Finally we provide the RVs measured with our procedure for the targets observed during GIANO Science Verification.     

Atomic oxygen in the comae of comets

We report on the detection of atomic oxygen lines in the spectra of 8 comets. These forbidden lines are a result of the photodissociation of the parent oxygen-bearing species directly into an excited state. We used high resolution spectra obtained at the McDonald Observatory 2.7 m telescope to resolve the cometary oxygen lines from the telluric oxygen lines and from other cometary emissions. We find that the relative intensities of the two red lines (6300.304 and 6363.776 Å) are consistent with theory. The green line (5577.339 Å) has an intensity which is about 10% of the sum of the intensities of the two red lines. We show that collisional quenching may be important in the inner coma. If we assume the relative excitation rates of potential parents which have appeared in the literature, then H₂O would be the parent of the cometary green oxygen line. However, those rates have been questioned. We measured the width of the three oxygen lines and find that the green line is wider than either of the two red lines. The finding of a wider line could imply a different parent for the green and red lines. However, the constancy of the green to red line flux ratio suggests the parent is the same for these lines but that the exciting photons have different energies.     

The symbiotic stellar lines at 6830 Å, 7088 Å; An origin in optically thick fluorescence

The question of the origin of the symbiotic stellar lines at 6830 Å and 7088 Å, recently proposed to arise from Raman scattering of ultraviolet Ovi lines by hydrogen, is examined quantitatively by comparing line intensities expected from this process with the intensity of an Feii line photoexcited by one of the same Ovi lines. It appears that Raman scattering does not yield sufficient intensity to account for the symbiotic lines. An alternative mechanism for producing the lines exists, however, in off-line-center photoexcitation of optically thick hydrogen by the Ovi lines. This gives intensities which are higher than Raman intensities, and which are more consistent with the Feii fluorescent line intensity. Observed further redward shifts are also explained by the mechanism. It is therefore suggested that the proposed hypothesis of Ovi–Hi interaction may be valid, but that the process involved is probably not second-order Raman scattering but first-order fluorescent scattering.     

Water vapor and Fe 5250.2

The commonly used magnetograph line of Fe 5250.2 Å is found to be weakly blended by telluric water vapor. This circumstance could bias solar rotation measurements.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

A complete photoelectric sunspot spectrum: An atlas from 3900–8000 Å

Complete photoelectric spectra of the photosphere as well as of both umbra and penumbra of a typical sunspot, ranging from 3900–8000 Å, have been obtained at the Locarno observatory. An automatic scanning device, a high precision electronic divider and an on-line Oscillomink penless recorder enabled us to eliminate the noise produced by image distortion and to scan the entire visible spectrum within just 5 h. The recordings have a linear dispersion of about 50 mm/Å and a spectral resolution of 40 mÅ or better. Simultaneously with these observations the momentary continuous spot intensity and its fast variation with time due to seeing variations have been recorded with a frequency resolution up to 100 Hz. In order to provide as much data as possible for the correction of the umbral spectrum for parasitic light, we also measured the limb profile and the aureola intensity at several wavelengths.At present, the recordings are being processed and combined into an atlas, which we plan to make available in either numerical or graphical form.As a first result, we compare our corrected continuous sunspot intensities with those of other authors and derive standard reference data on the radiation of both umbra and penumbra of a typical sunspot. Finally we make a comparison between some radiative properties of sunspots and late-type stellar atmospheres.     

Profiles of blue and infrared diffuse interstellar bands

The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) based on the extensive set of high-resolution spectra acquired with the aid of echelle spectrographs installed at the 2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyed diffuse interstellar bands cover the spectral ranges of blue and near-infrared, i.e the DIBs not surveyed by Krełowski & Schmidt . The possible modifications caused by stellar and telluric lines are discussed. The very broad features such as 4430 are not discussed because the shapes of their profiles, extracted from echelle spectra, are very uncertain. The signal-to-noise (S/N) ratios of the spectra are not high enough to enable discussion of the profiles of numerous weak interstellar features discovered recently.     

Sulphur abundances in halo stars from multiplet 3 at 1045 nm

Sulphur is a volatile α ‐element which is not locked into dust grains in the interstellar medium (ISM). Hence, its abundance does not need to be corrected for dust depletion when comparing the ISM to the stellar atmospheres. The abundance of sulphur in the photosphere of metal‐poor stars is a matter of debate: according to some authors, [S/Fe] versus [Fe/H] forms a plateau at low metallicity, while, according to other studies, there is a large scatter or perhaps a bimodal distribution. In metal‐poor stars sulphur is detectable by its lines of multiplet 1 at 920 nm, but this range is heavily contaminated by telluric absorptions, and one line of the multiplet is blended by the hydrogen Paschen ζ line. We study the possibility of using multiplet 3 (at 1045 nm) for deriving the sulphur abundance because this range, now observable at the VLT with the infra‐red spectrograph CRIRES, is little contaminated by telluric absorption and not affected by blends at least in metal‐poor stars. We compare the abundances derived from multiplets 1 and 3, taking into account NLTE corrections and 3D effects. Here we present the results for a sample of four stars, although the scatter is less pronounced than in previous analysis, we cannot find a plateau in [S/Fe], and confirm the scatter of the sulphur abundance at low metallicity (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the pseudo-resonance absorption lines in planetary nebulae

The possiblity of the excitation of a new class of spectral lines, so calledpseudo-resonance absorption lines in the conditions of planetary nebulae, is predicted. These lines are formed by permitted atomic transitions from the metastable levels to the upper subordinate, but not metastable, levels. To observe pseudo-resonance lines of nebular origin is possible only on the spectra of the nuclei of planetary and diffuse nebulae in the form of absorption lines.The preliminary list of pseudo-resonance lines is given in Table I; all of them are located in the region of vacuum ultra-violet (1000–3000 Å), therefore, their observation is possible only under space conditions.In stellar photospheres as well as in the interstellar medium the formation of pseudo-resonance lines is impossible.     

The transfer of polarized radiation in spectral lines: Solar-type stellar atmospheres

The polarization structure in several spectral lines in solar type stars is computed using the method described by McKenna (1981, 1984a). The frequency redistribution function used for these calculations is a linear combination ofR _II andR _III. The line profiles and polarization structures have been computed for several weak solar resonance lines includingKi 7664 Å, Sri 4607 Å, Baii 4554 Å, for various polar angles along the stellar disk. Both the line profiles and polarization structures as well as the center to limb behavior of the line center polarization agree well with observations.The somewhat stronger resonance line Cai 4227 Å shows a different polarization structure when compared to the weaker solar resonance lines. It is found that for strong resonance lines the proper redistribution function to be used is a linear combination ofR _III andR _v (see McKenna, 1981, 1984b; Heinzel, 1981). The major reason for this is that for strong resonance lines both the upper and lower levels are broadened by collisions. This violates the assumptions upon which the redistribution functionsR _II andR _III are based.     

EURD: The Mission and the Stellar Absolute Fluxes of B-Type Stars

We present here stellar spectra of B stars obtained with the EURD spectrograph, one of the three instruments on board MINISAT-01. EURD is a spectrograph specially designed to detect diffuse radiation in thewavelength range between 350 and 1100 Å with 5 Å spectral resolution. EURD main scientific targets are: the spectrum of interstellar medium,atmospheric airglow, decaying neutrinos, Moon and early type stars.     

Spectrum of the Extreme Ultraviolet Nightglow as Measured by EURD

After 2 years of operation onboard the Spanish satellite MINISAT, EURDhas achieved an unprecedented success in the observation of the terrestrialnightglow in the EUV, covering a range of 350-1100 Å EURD hasprovided a total of more than 543 hours ofintegration in the long wavelength spectrometer and more than898 hours in the short wavelength one, allowing the achievement of the most detailed atlas of the terrestrial EUV nightglow ever obtained. We present here the spectra obtained, together with the identification of the lines, some of themdetected for the first time in the nightglow. These spectrarepresent an improvement in sensitivity of several orders of magnitude with respect to previous observations. It has beenpossible, for the first time, to identify the complete Lymanseries of atomic hydrogen, resolving up to Lyman-. It hasalso been possible to identify the helium Lyman- line at 537 Å andto detect other lines of the blended Lyman series of helium, at 515 and522 Å. The spectra clearly show the presenceof the OII lines at 617, 644, 673, and 718 Å, previouslyobserved in the dayglow but seen here for the first time in thenightglow. In addition to the recombination continuum of the atomicoxygen at 911 Å, two features of OI have been detected in thenightglow: the 3s ³D_o transition at 989 Å, previouslyobserved by Chakrabarti (1984) and the 2p³4s³S^o transition at 1040 Å, partially overlapped with Lyman , but clearly distinguishable from it. This feature has been seen for the first timein the terrestrial nightglow. The radiative recombination continuum of atomic oxygen at 911 Å, that wasabsent in the observations of the first year of operation of EURD,is now clearly visible. The reasons of the absence of the OIfeature during the first year of operation are still unknown.Anderson et al. (1976) also noticed a strong variation with time of this 911 Å emission.     

The abundance of ammonia in the atmosphere of Jupiter

A laboratory curve of growth analysis was made on the lines in two ammonia bands located at 6450 Å and 10800 Å and the abundance of ammonia in the atmosphere of Jupiter was determined. Lines in the 6450 Å band appear to fall on the weak line section of the curve of growth, while those in the 10800 Å band fall in the transition region. The abundance values obtained from these bands are 13.0±3 m atm and 15±8 m atm, respectively.Measurements of the intensity distribution in the 6450 Å band in the laboratory and in the Jovian spectra show that the intensity of several lines in this band is highly dependent on the temperature. Strengths for some of the lines in the 6450 Å band were determined and half-widths of some strong lines were also measured. The effective pressure found from these half-width values is 2.5 atmospheres.Contributions from the University of Illinois, Chicago Circle Physics Department, No. 12.     

Characterization of zonal winds in the stratosphere of Titan with UVES

Titan has been observed with UVES, the UV-Visual Echelle Spectrograph at the Very Large Telescope, with the aim of characterizing the zonal wind flow. We use a retrieval scheme originally developed for absolute stellar accelerometry [Connes, P., 1985. Astrophys. Space Sci., 110, 211-255] to extract the velocity signal by simultaneously taking into account all the lines present in the spectrum. The method allows to measure the Doppler shift induced at a given point by the zonal wind flow, with high precision. The short-wavelength channel (4200-5200 Å) probes one scale height higher than the long-wavelength one (5200-6200 Å), and we observe statistically significant evidence for stronger winds at higher altitudes. The results show a high dispersion. Globally, we detect prograde zonal winds, with lower limits of 62 and 50 m s⁻¹ at the regions centered at 200 and 170 km altitude, but approximately a quarter of the measurements indicates null or retrograde winds.     

Comparison of unidentified absorption lines of quasar spectra with unidentified lines of stellar spectra

Conclusions Thus, we have considered the possibility of comparing unidentified lines of quasar spectra with unidentified lines of stellar spectra. Since the majority of absorption lines in the spectrum of Oph have wavelength shorter than 1000 Å, a comparison could be made in practice only with the absorption lines of Pup. Significant excesses in the number of coincidences over the mean level were not found, but in the case of the quasar 2351–154 the number of such coincidences within the reliable system is somewhat higher than for the other spectra. It is interesting that all the lines in the spectrum of this quasar that we distinguished belong to the unidentified lines.Of course, such comparison of the absorption lines of quasar spectra and the lines of stellar spectra can be regarded only as a weak attempt to win back in the L forest at least some lines for the absorption systems. However, for more distant absorption systems that could possibly be detected this method could play a more important part.Institute of Cosmic Research, USSR Academy of Sciences. Translated from Astrofizika, Vol. 38, No. 1, pp. 27–33, January–February, 1989.