The structure and kinematics of the the Galaxy thin gaseous disc outside the solar orbit

The rotation curve of the Galaxy is generally thought to be flat. However, using radial velocities from interstellar molecular clouds, which is common in rotation curve determination, seems to be incorrect and may lead to incorrectly inferring that the rotation curve is flat indeed. Tests basing on photometric and spectral observations of bright stars may be misleading. The rotation tracers (OB stars) are affected by motions around local gravity centers and pulsation effects seen in such early type objects. To get rid of the latter a lot of observing work must be involved. We introduce a method of studying the kinematics of the thin disc of our Galaxy outside the solar orbit in a way that avoids these problems. We propose a test based on observations of interstellar CaII H and K lines that determines both radial velocities and distances. We implemented the test using stellar spectra of thin disc stars at galactic longitudes of 135{\degr} and 180{\degr}. Using this method, we constructed the rotation curve of the thin disc of the Galaxy. The test leads to the obvious conclusion that the rotation curve of the thin gaseous galactic disk, represented by the CaII lines, is Keplerian outside the solar orbit rather than flat.Comment: 33 pages, 18 figures, accepted for publication in Publications of the Astronomical Society of the Pacific, 2015. February

A novel and sensitive method for measuring very weak magnetic fields of DA white dwarfs: A search for a magnetic field at the 250 G level in 40 Eri B

Searches for magnetic fields in white dwarfs have clarified both the frequency of occurrence and the global structure of the fields found down to field strengths of the order of 500 kG. Below this level, the situation is still very unclear. We are studying the weakest fields found in white dwarfs to determine the frequency of such fields and their structure. We describe a very sensitive new method of measuring such fields in DA (H-rich) white dwarfs, and search for a field in the brightest such star, 40 Eri B. Our new method makes use of the strongly enhanced polarisation signal in the sharp core of Halpha. We find that with one-hour integrations with the high-resolution spectropolarimeter ESPaDOnS on the 3.6-m CFHT, we can reach a standard error fo the longitudinal field of about 85 G, the smallest error ever achieved for any white dwarf. Nevertheless, we do not detect a magnetic field in this star. Observations with ISIS at the WHT, and the Main Stellar Spectrograph at the SAO, support the absence of a field at somewhat lower precision. The new method is very efficient; it is shown that for suitable DA stars the integration time, with ESPaDOnS on a 3.6-m telescope, to reach a 500 G standard error on a white dwarf of V = 12.5, is about half an hour, about the same as the time required on an ESO 8-m telescope with FORS using conventional low-resolution spectropolarimetry.Comment: Accepted by Astronomy & Astrophysics on 20/06/201

The Lorentz force in atmospheres of CP stars: 56 Arietis

The presence of electric currents in the atmospheres of magnetic chemically peculiar (mCP) stars could bring important theoretical constrains about the nature and evolution of magnetic field in these stars. The Lorentz force, which results from the interaction between the magnetic field and the induced currents, modifies the atmospheric structure and induces characteristic rotational variability of pressure-sensitive spectroscopic features, that can be analysed using phase-resolved spectroscopic observations. In this work we continue the presentation of results of the magnetic pressure studies in mCP stars focusing on the high-resolution spectroscopic observations of Bp star 56Ari. We have detected a significant variability of the Halpha, Hbeta, and Hgamma spectral lines during full rotation cycle of the star. Then these observations are interpreted in the framework of the model atmosphere analysis, which accounts for the Lorentz force effects. We used the LLmodels stellar model atmosphere code for the calculation of the magnetic pressure effects in the atmosphere of 56Ari taking into account realistic chemistry of the star and accurate computations of the microscopic plasma properties. The Synth3 code was employed to simulate phase-resolved variability of Balmer lines. We demonstrate that the model with the outward-directed Lorentz force in the dipole+quadrupole configuration is likely to reproduce the observed hydrogen lines variation. These results present strong evidences for the presence of non-zero global electric currents in the atmosphere of this early-type magnetic star.Comment: Accepted by A&A, 9 pages, 7 figures, 2 table

Centrosymmetric molecules as possible carriers of diffuse interstellar bands

In this paper, we present new data with interstellar C2 (Phillips bands A-X), 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 C2 for nine Galactic lines. For seven of these, C2 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 C2 excitation has been made, has increased significantly. This paper is a continuation of previous works where interstellar molecules (C2 and diffuse interstellar bands) have been analysed. Because the sample of interstellar clouds with C2 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 C2; the profiles are broader because of the higher values of the gas kinetic and rotational temperatures of C2. There are also diffuse interstellar bands (4964 and 5850 A) for which this effect does not exist.Comment: 8 pages, 4 figures, accepted to MNRAS 201

The chemical composition of a mild barium star HD202109

We present the result of chemical abundances of a mild barium star HD202109 (zeta Cyg) determined from the analysis of spectrum obtained by using a 2-m telescope at the Peak Terskol Observatory and a high-resolution spectrometer with R=80,000, signal to noise ratio >100. We also present the atmospheric parameters of the star determined by using various methods including iron-line abundance analysis. For line identifications, we use whole-range synthetic spectra computed by using the Kurucz database and the latest lists of spectral lines. Among the determined abundances of 51 elements, those of P, S, K, Cu, Zn, Ge, Rb, Sr, Nb, Mo, Ru, Rh, Pd, In, Sm, Gd, Tb, Dy, Er, Tm, Hf, Os, Ir, Pt, Tl, and Pb have not been previously known. Under the assumption that the overabundance pattern of Ba stars is due to wind-accretion process, adding information of more element abundances enables one to show that the heavy element overabundances of HD202109 can be explained with the wind accretion scenario model.Comment: 10 pages, Accepted by Astronomy and Astrophysic

Detection of vibronic bands of C3_3 in a translucent cloud towards HD 169454

We report the detection of eight vibronic bands of C$_3$, seven of which have been hitherto unobserved in astrophysical objects, in the translucent cloud towards HD~169454. Four of these bands are also found towards two additional objects: HD~73882 and HD~154368. Very high signal-to-noise ratio ($\sim$1000 and higher) and high resolving power ($R=80,000$) UVES-VLT spectra (Paranal, Chile) allow for detecting novel spectral features of C$_3$, even revealing weak perturbed features in the strongest bands. The work presented here provides the most complete spectroscopic survey of the so far largest carbon chain detected in translucent interstellar clouds. High-quality laboratory spectra of C$_3$ are measured using cavity ring-down absorption spectroscopy in a supersonically expanding hydrocarbon plasma, to support the analysis of the identified bands towards HD~169454. A column density of N(C$_3$) = $(6.6 \pm 0.2) \times 10^{12}$ cm$^{-2}$ is inferred and the excitation of the molecule exhibits two temperature components; $T_{exc}= 22 \pm 1$ K for the low-$J$ states and $T_{exc}= 187 \pm 25$ K for the high-$J$ tail. The rotational excitation of C$_3$ is reasonably well explained by models involving a mechanism including inelastic collisions, formation and destruction of the molecule, and radiative pumping in the far-infrared. These models yield gas kinetic temperatures comparable to those found for $T_{exc}$. The assignment of spectral features in the UV-blue range 3793-4054 \AA\ may be of relevance for future studies aiming at unravelling spectra to identify interstellar molecules associated with the diffuse interstellar bands (DIBs).Comment: 15 pages, 13 figures, submitted to MNRA