F. A. Musaev

Narrow Diffuse Interstellar Bands: A Survey with Precise Wavelengths

We present an atlas of 271 diffuse interstellar bands (DIBs) between 4460 and 8800 A based on echelle spectra (R = 45,000), of which more than 100 are new DIBs discovered in this survey. The atlas is restricted mostly to narrow features, and we describe the tests for an interstellar origin. The rest wavelength of each DIB was determined in a high-quality composite spectrum of the star HD 23180 using the interstellar Na i (D1 and D2) lines to establish the radial velocity of the single intervening cloud. DIB wavelengths are quoted to 0.01 A and are probably accurate to ~0.1 A. Other, weak DIBs found in the spectra of heavily reddened stars are included with a lower wavelength precision.

High-Resolution Spectroscopy of the Yellow Hypergiant ρ Cassiopeiae from 1993 through the Outburst of 2000-2001

We present an overview of the spectral variability of the peculiar F-type hypergiant ρ Cas, obtained from our long-term monitoring campaigns over the past 8.5 yr with four spectrographs in the northern hemisphere. Between 2000 June and September an exceptional variability phase occurred when the V brightness dimmed by about a full magnitude. The star recovered from this deep minimum by 2001 April. It is the third outburst of ρ Cas on record in the last century. We observe TiO absorption bands in high-resolution near-IR spectra obtained with the Utrecht Echelle Spectrograph during the summer of 2000. TiO formation in the outer atmosphere occurred before the deep brightness minimum. Atmospheric models reveal that the effective temperature decreases by at least 3000 K, and the TiO shell is driven supersonically with 5.4 × 10-2 M☉ yr-1. Strong episodic mass loss and TiO have also been observed during the outbursts of 1945-1947 and 1985-1986. A detailed analysis of the exceptional outburst spectra is provided, by comparing with high-resolution optical spectra of the early M-type supergiants μ Cep (Ia) and Betelgeuse (Iab). During the outburst, central emission appears above the local continuum level in the split Na D lines. A prominent optical emission line spectrum appears in variability phases of fast wind expansion. The radial velocity curves of Hα and of photospheric metal absorption lines signal a very extended and velocity-stratified dynamic atmosphere. The outburst spectra indicate the formation of a low-temperature, optically thick circumstellar gas shell of 3 × 10-2 M☉ during 200 days, caused by dynamic instability of the upper atmosphere of this pulsating massive supergiant near the Eddington luminosity limit. We observe that the mass-loss rate during the outburst is of the same order of magnitude as has been proposed for the outbursts of η Carinae. We present calculations that correctly predict the outburst timescale, whereby the shell ejection is driven by the release of hydrogen ionization recombination energy.

The relation between CH and CN molecules and carriers of 5780 and 5797 diffuse interstellar bands

Optical absorption bands of the interstellar CN (near 3875 A) and CH molecules (the violet and blue ones near 4300 and 3886 A, respectively) were applied to determine the column densities of these two radicals in a statistically meaningful sample of 84 reddened OB stars. Equivalent widths of the major 5780 and 5797 diffuse bands (DIBs) were measured along the lines of sight toward the same stars in spectra acquired using four echelle spectrographs situated in both the northern and southern hemispheres. The mutual relation between abundances of CH and CN molecules shows a large scatter; and especially the CN molecule abundance varies strongly from cloud to cloud. The carriers of the major 5780 and 5797 DIBs seem to be spatially correlated with column densities of CH rather than of the CN molecule. This is most likely true in the case of a narrower feature: the 5797 DIB correlates with CH column density better than 5780 does. The correlations do suggest that the DIB carriers are likely hydrocarbons. They apparently occupy molecular clouds since the H 2 abundance is closely related to that of methylidyne (CH), as has already been demonstrated.

Interstellar Ca II Line Intensities and the Distances of the OB stars

We show that the equivalent widths of the well-known interstellar Ca II H and K lines can be used to determine the distances to OB stars in our Galaxy. The equivalent widths, measured in the spectra of 147 early-type stars, are strongly related to the Hipparcos parallaxes of those objects. The lines fitted to the parallax-equivalent width data are given by the formulae π = 1/ and π = 1/ , where π is in arcseconds and EW is in milliangstroms. The form of the formulae, yielding a finite parallax even for zero absorption, shows that space within ≈100 pc of the Sun contains very little Ca II, which is in agreement with the known dimensions of the Local Bubble. Using Ca II lines for distance determination does not require the knowledge of the absolute magnitude of the object; it is thus well suited for targets for which the absolute calibration is either not precise (OB supergiants) or not available at all (peculiar objects). We also demonstrate that neither the reddening E(B - V) nor the equivalent widths of interstellar K I and CH lines are suitable candidates for distance estimation, their relation with parallaxes being far less tight than for Ca II.

Diffuse Interstellar Bands: Physical Conditions That Facilitate the Formation or Preservation of Their Carriers

This paper suggests that the formation and/or preservation of the carriers of at least some of the diffuse interstellar bands (DIBs) depends on the level of ionization of certain interstellar atoms, such as potassium and calcium inside H I clouds. The spectral lines of these elements are apparently well correlated with the narrow diffuse bands, such as 5797 or 6379 A. Thus, the physical conditions that facilitate the growing abundance of neutral alkali atoms also facilitate the formation or preservation of the carriers of the narrow diffuse bands. The broad features, such as 5780 or 6284 A, apparently originate in different ionization conditions.

Relation between CH cation and neutral/molecular hydrogen (Research Note)

Observations of interstellar absorption bands of CH + molecule at 3957 and 4232 A were applied to determine column densities toward 53 stars. The targets were selected because the atomic and molecular hydrogen column densities are published. The data on CH + were acquired using four echelle spectrographs situated in both the Northern and Southern hemispheres. Spatial relations between column densities of CH + and those of molecular, atomic and total hydrogen show large scatter, suggesting there is no relation between abundances of methylidyne cation and hydrogen in any form.

Observational test of the CH cation oscillator strengths

We revise measurements of the positions and oscillator strengths using spectral features in the CH + A - X system, and by using high-resolution, echelle spectra of 36 stars and assuming that its wavelength and oscillator strength as given in the literature for the (0,0) transition, i.e. 4232.548 A and 0.00545 respectively, are correct. The recommended oscillator strengths of the lines at 3957.689, 3745.308, 3579.024, and 3447.077 A are found to be (in units of 10 -5 ) 342, 172, 75, and 40, respectively. The estimated column densities of the CH cation toward the observed targets are also presented.

Centrosymmetric molecules as possible carriers of diffuse interstellar bands

In this paper, we present new data with interstellar C 2 (Phillips bands A 1 Π u -X 1 ∑ + g ), from observations made with the Ultraviolet-Visual Echelle Spectrograph of the European Southern Observatory. We have determined the interstellar column densities and excitation temperatures of C 2 for nine Galactic lines. For seven of these, C 2 has never been observed before, so in this case the still small sample of interstellar clouds (26 lines of sight), where a detailed analysis of C 2 excitation has been made, has increased significantly. This paper is a continuation of previous works where interstellar molecules (C 2 and diffuse interstellar bands) have been analysed. Because the sample of interstellar clouds with C 2 has increased, we can show that the width and shape of the profiles of some diffuse interstellar bands (6196 and 5797 A) apparently depend on the gas kinetic and rotational temperatures of C 2 ; the profiles are broader because of the higher values of the gas kinetic and rotational temperatures of C 2 . There are also diffuse interstellar bands (4964 and 5850 A) for which this effect does not exist.

DYNAMICAL PHENOMENA IN THE ATMOSPHERE OF THE PROTO-PLANETARY NEBULA IRAS 22272+5435

Radial velocity monitoring of the star HD 235858 confirmed regular variations with a peak-to-peak amplitude of about 10 km s–1 and a period of about 131.2 days. The light, color, and velocity variations are typical for RV Tauri stars. Splitting of low-excitation atomic lines was detected. The components are both blue- and redshifted relative to the systemic velocity. Significant variations are observed in the intensity of C2 and CN lines. Variable emission in the Hα profile, splitting of low-excitation atomic absorption lines, appearance of CN emission lines, blue wings of strong lines, and recent reddening give evidence of shocks and mass outflow obviously induced by atmospheric pulsations.

The Structure and Kinematics of the Galaxy Thin Gaseous Disk Outside the Solar Orbit

The rotation curve of the Galaxy is generally thought to be flat. However, using radial velocities from interstellar molecular clouds, as is common in rotation curve determination, seems to be incorrect and may lead to wrongly inferring that the rotation curve is flat indeed. Tests based on photometric and spectral observations of bright stars may also be misleading. The rotation tracers (OB stars) are affected by motions around local gravity centers and by pulsation effects seen in such early-type objects. To get rid of the latter involves extensive observing work. We introduce a method of studying the kinematics of the thin disk of our Galaxy outside the solar orbit in a way that avoids these problems. We propose a test based on observations of interstellar Ca ii H and K lines that determines both radial velocities and distances. We implemented the test using stellar spectra of thin disk stars at Galactic longitudes of 135° and 180°. Using this method, we constructed the rotation curve of the thin disk of the Galaxy. The test leads to the obvious conclusion that the rotation curve of the thin gaseous galactic disk, represented by the Ca ii lines, is Keplerian outside the solar orbit rather than flat.