Search

We report on the stellar content, half-light radii and star formation rates of a sample of 10 known high-redshift ($z\gtrsim 2$) galaxies selected on strong neutral hydrogen (HI) absorption (log(N(HI)/cm$^{-2})>19$) toward background quasars. We use observations from the {\it Hubble Space Telescope} (HST) Wide Field Camera 3 in three broad-band filters to study the spectral energy distribution(SED) of the galaxies. Using careful quasar point spread function subtraction, we study their galactic environments, and perform the first systematic morphological characterisation of such absorption-selected galaxies at high redshifts. Our analysis reveals complex, irregular hosts with multiple star-forming clumps. At a spatial sampling of 0.067 arcsec per pixel (corresponding to 0.55 kpc at the median redshift of our sample), 40% of our sample requires multiple S��rsic components for an accurate modelling of the observed light distributions. Placed on the mass-size relation and the `main sequence' of star-forming galaxies, we find that absorption-selected galaxies at high redshift extend known relations determined from deep luminosity-selected surveys to an order of magnitude lower stellar mass, with objects primarily composed of star-forming, late-type galaxies. We measure half-light radii in the range $r_{1/2} \sim$ 0.4 to 2.6 kpc based on the reddest band (F160W) to trace the oldest stellar populations, and stellar masses in the range $\log (\mathrm{M}_{\star}/\mathrm{M}_{\odot}) \sim$ 8 to 10 derived from fits to the broad-band SED. Spectroscopic and SED-based star formation rates are broadly consistent, and lie in the range log(SFR/M$_{\odot} $yr$^{-1}$) $\sim$0.0 to 1.7., 17 pages, Accepted for publication in MNRAS. This revision has minor text changes

We present new 14 high-resolution echelle spectra to discuss the level of chromospheric activity of DM UMa in {He I} D3, {Na I} D1, D2, Halpha, and {Ca II} infrared triplet lines (IRT). It is the first time to discover the emissions above the continuum in the {He I} D3 lines on 2015 February 9 and 10. The emission on February 9 is the strongest one ever detected for DM UMa. We analysed these chromospheric active indicators by employing the spectral subtraction technique. The subtracted spectra reveal weak emissions in the {Na I} D1, D2 lines, strong emission in the Halpha line, and clear excess emissions in the {Ca II} IRT lines. Our values for the EW8542/EW8498 ratio are on the low side, in the range of 1.0-1.7. There are also clear phase variations of the level of chromospheric activity in equivalent width (EW) light curves in these chromospheric active lines (especially the Halpha line). These phenomena might be explained by flare events or rotational modulations of the level of chromospheric activity., 8 pages, 10figures

High-dispersion IUE spectra of six late-type stars exhibit small but statistically significant differential redshifts of high-temperature emission lines, like Si IV and C IV, with respect to low-temperature lines like S I and O I. A well-exposed, small-aperture spectrum of the active chromosphere binary Capella (Alpha Aurigae A: G6 II+F9 III) establishes that the high-temperature lines are redshifted in an absolute sense with respect to the accurately determined photospheric velocity of the system at single-line phase 0.50. Several possible explanations for the stellar redshifts are discused, including a warm wind (100,000 K) in which aparent redshifts are produced in optically thick lines by an accelerating outfow, and the downflowing component of a vertical circulation system for which the up-leg portion of the flow is too cool, too hot, or too tenuous to be visible in Si IV and C IV. If the second scenario is true, the stellar redshifts may provide an important phenomenological link to the downflows observed in 100,000 K species over magnetic active regions in the sun.

The photometric properties of the late-type star PZ Mon are analysed assuming the presence of spots on its surface. The long-term variability in brightness is considered using photographic data together with photoelectric data in the B band. The combined light curve covers the time span from 1898 to 2004 and shows two deep minima which might be interpreted as an activity cycle with a period of 50 years. The investigation of seasonal variations is based on UBVRI observations carried out with the 1.25 m telescope at the Crimean Astrophysical Observatory in 1992–2004. The derived colours of PZ Mon indicate that the spectral type of the star is K5 and therefore the parameters of spots were calculated adopting a value for the temperature of the photosphere of 4800 K. Applying the simple model of star spots we found that a seasonal variability can be produced by spots which cover 17–30% of the hemisphere. The spot temperatures are constant and close to 2700 K. If the deep minima on the long-term curve are also ...

NN Ser is known to be a 17 mag pre-cataclysmic binary consisting of a hot white dwarf and a cool late type star orbiting each other with a period of 3$^{{\rm h}}$ 7$^{{\rm m}}$. The system shows very deep eclipses and a pronounced reflection effect. Using the FORS instruments at the VLT the late type star could now be detected photometrically at 22.8 mag during eclipse and monitored spectroscopically. These data combined with earlier high speed photometric and phase-resolved spectroscopic observations form the basis for a determination of refined system parameters for NN Ser. The spectral type of the late type star is found to be M4.75. A model atmosphere analysis of the white dwarf yields a temperature of 57 000 ± 3000 K and log g = 7.6 ± 0.1. The presence of He in the atmosphere ($N_\mathrm{He} = 2\pm0.5\times10^{-4}$ by number) indicates that the white dwarf is a hydrogen-helium hybrid star of type DAO1. Since the derived radial velocity curves prevent an unambiguous determination of the mass ratio the white dwarf's mass of 0.54 ± 0.05 $M_{\odot}$ is inferred using the results of the model atmosphere analysis and recent evolutionary models. The mass of the M star is determined via a well calibrated M-R relation to be 0.150 ± 0.008 $M_{\odot}$. The photometric measurements are analysed using a sophisticated light curve synthesis program and yield the following results: i = 84.6° ± 1.1°, $R_{{\rm wd}}$ = 0.0189 ± 0.0010 $R_{\odot}$, and $R_{{\rm M star}}$ (polar) = 0.174 ± 0.009 $R_{\odot}$. The shape of the cool star turns out to be slightly ellipsoidal. Its temperature at the un-heated hemisphere (backside) is 2 920 ± 70 K while the heated hemisphere (sub-stellar point) has a temperature of 7125 ± 200 K.

We present the first L-band spectroscopic observations for a dozen stellar sources in the central 0.5 pc of the GC stellar cluster that are bright in the 2-4 micron wavelength domain. With the aid of additional K-band spectroscopic data, we derive optical depth spectra of the sources after fitting their continuum emission with a single reddened blackbody continuum. We also derive intrinsic source spectra by correcting the line of sight extinction via the optical depth spectrum of a late type star that is most likely not affected by local dust emission or extinction at the Galactic Center. The good agreement between the two approaches shows that the overall variation of the line-of-sight extinction across the central 0.5 pc is $\Delta A_{\mathrm{K}}\leq0.5$ mag. The extinction corrected spectra of the hot He-stars are in good agreement with pure Rayleigh Jeans continuum spectra. The intrinsic spectra of all other sources are in agreement with continuum emission and absorption features due to the dust in which they are embedded. We interprete both facts as evidence that a significant amount of the absorption takes place within the central parsec of the Galactic Center and is most likely associated with the individual sources there. We find absorption features at 3.0 micron, 3.4 micron, and 3.48 micron wavelength. Correlations between all three features show that they are very likely to arise in the ISM of the central 0.5 pc. Spectroscopy of high MIR-excess sources 0.5'' north of the IRS 13 complex is largely consistent with them being YSOs. However, a bow-shock nature of these sources cannot be excluded., Comment: 19 pages. 19 figures. 6 tables. Accepted in A&A

We present the last pointed observation of AM Her carried out during the life of the BeppoSAX satellite. It was bright at the beginning of the observation, but dropped to the lowest X-ray level ever observed so far. The X-ray emission during the bright period is consistent with accretion occurring onto the main pole of the magnetized white dwarf. The rapid change from the active state to the low deep state indicates a drop by a factor of 17 in the accretion rate and hence that accretion switched-off. The short timescale (less than one hour) of this variation still remains a puzzle. Optical photometry acquired simultaneousy during the low state shows that the white dwarf remains heated, although a weak emission from the accretion stream could be still present. Cyclotron radiation, usually dominating the V and R bands, is negligible thus corroborating the possibility that AM Her was in an off-accretion state. The X-ray emission during the inactive state is consistent with coronal emission from the secondary late type star., 6 pages A&A-Latex, 6 Figures, accepted for publication in A&A

We present low and high resolution long-slit spectra of three bipolar planetary nebulae (PNe) with bright central cores: A79, He2-428 and M1-91. He2-428 and M1-91 have high density (from 10^3.3 to 10^6.5 cm^-3) unresolved nebular cores that indicate that strong mass loss/exchange phenomena are occurring close to their central stars. An F0 star is found at the centre of symmetry of A79; its reddening and distance are consistent with the association of the star with the nebula. The spectrum of the core of He2-428 shows indications of the presence of a hot star with red excess emission, probably arising in a late-type companion. A79 is one of the richest PNe in N and He, the abundances of M1-91 are at the lower end of the range spanned by bipolar PNe, and He2-428 shows very low abundances, similar to those measured for halo PNe. The extended nebulae of A79 and He2-428 have inclined equatorial rings expanding at a velocity of approx. 15 km/s, with kinematical ages 10^4 yr. The association of these aged, extended nebulae with a dense nebular core (He2-428) or a relatively late type star (A79) is interpreted as evidence for the binarity of their nuclei., Comment: 13 pages including 8 tables. A&A accepted; also available at http://www.iac.es/publicaciones/preprints.html

A SiO maser survey in the J =1 0, v = 1 and 2 transitions has been made for IRAS sources in the North Galactic Cap (b > 30) with the Nobeyama 45 m radio telescope. The sources were selected on the basis of their IRAS 12/25-m and 25/60-m flux ratios as likely oxygen-rich AGB candidates. SiO masers were detected from 24 out of the 97 selected sources, where 17 were new detections. The distances and heights above the Galactic plane are calculated. The Galactic distribution of detected and undetected stars indicates that metallicity is likely to govern the detection rate. The Galactocentric angular velocities of the subsampled stars are derived and their variation with the Galactic height is discussed.

We present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius determined from finite-source effects, we estimate the physical parameters of the lens system. We find that the event was caused by a $2.73\pm 0.43\ M_{\rm J}$ planet orbiting a $0.44\pm 0.07\ M_{\odot}$ early M-type star. The distance to the lens is $4.97\pm 0.29$\ kpc and the projected separation between the host star and its planet at the time of the event is $3.45\pm 0.26$ AU. We find that the additional coverage provided by follow-up observations, especially during the planetary perturbation, leads to a more accurate determination of the physical parameters of the lens., 9 pages, 4 figures, accepted by ApJ

We have obtained low-resolution (λ/Δλ ∼ 160) 3-μm spectra of a selection of field stars lying behind the Taurus dark cloud. Several of these stars have abnormal extinction laws, which are best characterized by A K ≤ 0.27E(J−K) and A V ≤ 5.4 E(J−K). We find a very good correlation between A V and τ 3.05 (the H 2 O ice feature), confirming a previous result, and between A V and τ 3.45 (the long-wavelength wing), yielding the ratios τ 3.05 /A V = 0.059 ± 0.003 and τ 3.45 /A V = 0.0077 ± 0.0005. The threshold extinctions for the H 2 O ice band and the long-wavelength wing are found to be the same, within the uncertainties, at A v0 = 2.6. The fact that these thresholds are the same means that the long-wavelength wing cannot be a result of a highly refractory hydrocarbon residue

The APM facility in Cambridge has been used to search archive UK Schmidt Telescope photographic plates for an optical counterpart of SGR 1806-20. The search has revealed a late-type variable star just outside the revised 3 σ error box. A low-resolution spectrum of the star suggests that it is almost undoubtedly an M9 Mira

We present a photometric study of 11 G-K dwarf members of the young open cluster surrounding α Persei, whose projected rotational velocities have indicated them to be rapid rotators. We detect significant rotational modulation due to surface inhomogeneities in 10 of the targets. We determine reliable axial rotation periods for six of these stars, using power spectrum analysis augmented with the CLEAN algorithm. Similar period analysis is also given for a further member whose power spectrum yielded ambiguous results

Models of the formation, evolution and structure of the solar cylinder are constructed on the basis of a large set of observational data on mainly late-type stars. Star formation in the disc is modelled with a simple, phenomenological prescription of the Schmidt type: Σ#78 * ∞Σ g N , N = 1-2. Models with a threshold for star formation are also considered. Infall of halo gas is assumed to happen on a characteristic time-scale t i . The results obtained are largely independent of the star formation prescription. For the best-fitting model (N = 1), we find that the age of the solar cylinder is t 0 = 11.8 ± 1.0 Gyr and that t i = 3.4 ± 0.4 Gyr

High-resolution spectra of the chromospheric Na I D lines, Ca I 4227, Mg I 4571, 5167, and 5172, the Ca II H and K resonance and IR 8542.144 and 8662.170 lines, and H-alpha and H-beta, all observed simultaneously at the AAT, are presented. These data are presented as the observational basis for the self-consistent, semiempirical modeling of the outer photospheres and chromospheres of the target stars. Stellar activity is found in the low-chromosphere lines as core-filling and, in some stars, as line-broadening. Integrated fluxes are derived from the difference spectra, formed by subtracting quiet from active spectra, in the Ca II H and K resonance and IR 8542 and 8662 lines and in H-alpha, which are presented as chromospheric activity indicators. All the activity indices exhibit strong correlations, with the exception of the equivalent widths of H-alpha and H-beta, which are found to be relatively poor activity discriminators.

We test the hypothesis that methane is the source of the carbon observed in carbon-bearing molecules around oxygen-rich stars, by considering the synthesis of formaldehyde which is formed in the reaction between oxygen atoms and methyl radicals. We find that, provided that the parent methane abundance is large enough, millimetre-wave emission lines of H 2 CO should be detectable in such stars. We also consider the formation of other species, notably H 2 CN and H 2 CS, from methyl radicals, but conclude that they will be at least one order of magnitude less abundant than H 2 CO and therefore not detectable with current instrumentation

The anomalously rapid decrease in the surface rotation rates of G dwarfs between the ages of the α Persei and Pleiades clusters has been attributed by some authors to the temporary decoupling of the convective envelope from the radiative interior. We investigate the implications of this suggestion for the evolution of the rotational velocity distributions in open clusters using a parametrized model of standard magnetic braking with varying strength of core-envelope coupling. We find that for solar-type stars only a weak coupling model, in which little of the angular momentum stored in the core of a fast rotator has been transferred to the envelope by the age of the Hyades, can provide a reasonable fit to the observed rotational distributions at the ages of the α Per, the Pleiades and the Hyades clusters

We report the discovery of a new short-period, main-sequence, chromospherically active late-type binary system. EUV observations performed by the ROSAT Wide Field Camera have identified the late-type star GL 841 A as a possible very active star by virtue of a large EUV-to-bolometric flux ratio. Subsequent optical observations at the wavelengths of the Hα and Ca II H and K lines have confirmed this, and also the binary nature of the system. An orbital period of 1.124 d, an inclination of 28° and a mass ratio of approximately unity are deduced from radial velocity data

The aim of this study is to investigate the physical properties of molecular envelopes of planetary nebulae in their earliest stages of evolution. Using the 100m telescope at Effelsberg, we have undertaken a high sensitivity discrete source survey for the first excited state of OH maser emission (J=5/2, 2PI3/2 at 6GHz) in the direction of planetary and proto-planetary nebulae exhibiting 18cm OH emission (main and/or satellite lines), and we further validate our detections using the Nan\c{c}ay radio telescope at 1.6-1.7GHz and MERLIN interferometer at 1.6-1.7 and 6GHz. Two sources have been detected at 6035MHz (5cm), both of them are young (or very young) planetary nebulae. The first one is a confirmation of the detection of a weak 6035MHz line in Vy 2-2. The second one is a new detection, in K 3-35, which was already known to be an exceptional late type star because it exhibits 1720MHz OH emission. The detection of 6035MHz OH maser emission is confirmed by subsequent observations made with the MERLIN interferometer. These lines are very rarely found in evolved stars. The 1612MHz masers surround but are offset from the 1720 and 6035MHz masers which in turn lie close to a compact 22GHz continuum source embedded in the optical nebula., Comment: 9 pages, 7 figures, published in A&A

Recent observations of brightness variations on the sun during the solar cycle have motivated us to re-examine the widely held view that cool, dark starspots, covering a significant fraction of the star, are the centers of magnetic activity on BY Dra stars. We propose that the magnetic regions are better described by a bright facular network, and that the dark areas which give rise to photometric rotational modulation are actually regions where the underlying quiet photosphere is seen. This interpretation is consistent with recent observations of late-type stars that show that bright areas covering much of the star have magnetic fields with strengths of several thousand gauss. It resolves several problems with the current model, including the size, location, and stability of the starspots required to match photometric and Doppler-imaging observations. It also has interesting observational implications for the correlation of photometric rotational modulation and long term brightness variations with other surface activity, and for the positions of magnetically active stars in the H-R diagram.

The JHKL' photometry and 2.3–4 μm spectrophotometry of some M giants, S type stars and carbon stars are presented in this paper. It is found that in combination with IRAS data, the energy spectra in 1–100 μm of S type stars are intermediate between those of M giants and carbon stars, which are obviously different. The spectrophotometry in the near infrared shows that, besides carbon stars, which have HCN and C2H2 strong absorptions at 3.1 μm, some S type stars have the similar but weaker absorption in the same spectral region. However, no trace of any absorption at 3.1 μm can be seen in M giants. These results probably provide more evidence for the M-S-C sequence in the late stage of stellar evolution.

Photometric data, covering a span of two and a half years, have been analysed for the chromospherically active giant star HD 86005. It was found to undergo light variations and a photometric period of 89.0 ± 0.3 days was determined. Evidence suggests that these brightness variations are due to the rotation of unevenly distributed starspots.

If the zero-age main sequence is expressed in the (V−I) versus (B−V)−(V−I) plane the reddening lines are found to lie at a great enough angle to allow reasonably accurate spectral-type classification for stars later than ∼F5. Earlier spectral types can also be identified but with lower accuracy. Comparisons with the Q method of UBV photometry and with spectra of some of the programme stars show that the BVI c technique produces reliable results

Based on IRAS photometric data, low resolution spectra, near-infrared photometric data, visible spectral features, main abundance ratios of MSC stars and physico-chemical processes taking place in their interior, we discuss their possible evolutionary states, pointing out that both the sequence M → S → C and the direct sequence M → C are possible.

The Australia Telescope Compact Array (ATCA) has been used to make 4.8-GHz observations of 24 fields containing post-main-sequence stars. These stars were selected from a sample of late-type (spectral types G, K and M) giants and bright giants within 30 pc claimed by Slee et al. (1989, MNRAS, 239), from observations with the Parkes radio telescope, to be variable non-thermal radio emitters. No significant 4.8 GHz radio emission was detected from these stars. Non-detection of any stars with the ATCA is an improbable result (given the claimed Parkes detection rates and the superior sensitivity of the ATCA) and calls for a re-analysis of the original Parkes 8.4-GHz observations

New atomic data are used to calculate the relative intensities of transitions within the Si II 3s 2 3p 2 P−3s3p 2 4 P intercombination multiplet for plasma parameters appropriate to late-type stellar atmospheres. These ratios are found to be significantly different from those of Dufton & Kingston (1991, MNRAS, 209), principally due to changes in the radiative rates. A comparison with line ratios for the Sun (from Skylab S082B spectra) and late-type stars (from IUE data) indicates that although the new theoretical line ratios are in better agreement with observation, significant discrepancies still exist. Possible explanations for these discrepancies are briefly discussed

We give results of near infrared observations of 17 stars of different OH maser types including their J, H and K magnitudes and fluxes. Their IRAS conterparts are identified. From a simultaneous analysis of their near infrared, far infrared and OH radio data we derive their near and far infrared luminosities L1 and L2, infrared gradients S1, characteristics S10 of the silicate 10 μ feature and the mass loss rate of the central star M. We found that, for all OH maser types, L1, L2, S1 and S10 all tend to increase with increasing mass loss rate. This shows that, for the red giants in the AGB sub-branch, there exists indeed a tightly connected evolutionary sequence from optical Mira stars to optically invisible OH/IR stars, from OH-1665/1667 masers to OH-1612 masers.

We review the recent development of observations of molecules in circumstellar envelopes of evolved stars. The large collecting areas and high spatial resolution of newly constructed radio telescopes have provided a resurgence of research in this area. Many molecules bearing silicon atoms, and heavier metals have been found. Observations with a spatial resolution of a few arcseconds have become possible by millimeter wave interferometers, giving us detailed information on the structure of the circumstellar envelopes. Especially bipolar and spherical flows in stars with large mass loss rates have been extensively mapped in various molecular lines. It has been recognized that molecular abundances are affected by ion-molecule reactions in the outer envelope. The theoretical evolutionary tracks from red giants to planetary nebulae have been confirmed further by detecting stars in a transition phase between oxygen- and carbon-rich atmospheres.

International audience; A Doppler image of the zero-age main-sequence (ZAMS) late-type rapidly rotating star LO Pegasi, based on spectra acquired between 2003 September 12 and 15 is presented. The least-squares deconvolution technique is applied to enhance the signal-to-noise ratio of the mean rotational broadened line profiles extracted from the observed spectra. In the present application, an unbroadened spectrum is used as a reference, instead of a simple line list, to improve the deconvolution technique applied to extract the mean profiles. The reconstructed image is similar to those previously obtained from observations taken in 1993 and 1998, and shows that LO Peg photospheric activity is dominated by high-latitude spots with a non-uniform polar cap. The latter seems to be a persistent feature as it has been observed since 1993 with little modifications. Small spots, observed between ~10° and ~60° of latitude, appears to be different with respect to those present in the 1993 and 1998 maps. Based on observations made with the Italian Telescopio Nazionale Galileo operated on the island of La Palma by the Centro Galileo Galilei of INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque del los Muchachos of the Instituto de Astrofísica de Canarias. E-mail: nicolo.piluso@oact.inaf.it (NP); nuccio.lanza@oact.inaf.it (AFL); isabella.pagano@oact.inaf.it (IP); alessandro.lanzafame@oact.inaf.it (ACL); donati@ast.obs-mip.fr (J-FD)

We present a dynamo model for the overshoot region between the convection zone and the radiative zone of a late type star. In the companion paper, Gilman and DeLuca above, we discussed some of the difficulties associated with convection zone dynamos. Section three of that paper, and in references therein, examines the physical processes that contribute to a dynamo in the overshoot layer. This paper will show how the model equations are derived and will discuss some of the solutions of those equations. A detailed derivation of the model equations will be given in a forthcoming paper.

A program of the accurate measurement of radial velocity variations has been started for the various stars using a Fabry-Perot interferometer at Okayama Astrophysical Observatory since 1986 to diagnose the internal structure of stars. In particular, we have accumulated such data for the late type star α CMi, which might have the largest amplitude of “Five-minute oscillations” according to the theoretical prediction (Ando 1976). Here we will give a brief explanation of the instrument and the data reduction procedure. The power spectrum for a time series of radial velocity variations in α CMi has been calculated. The noise level in this spectrum has been estimated to be about 10 m s−1. At this level, it is safe to say that any significant signal related to the stellar oscillations may not be detected. To confirm the “Five-minute oscillations” in this star, we should continue to reduce the noise level by improving the sensitivity of the instrument and/or by accumulating data moreover.

Photometry from a fourth season of observing at Van Vleck Observatory is reported for several T Tauri stars. Spectra have been obtained using the Image Tube Scanner on the 40” Nickel telescope at Lick Observatory for some of these stars. Both photometric and spectroscopic observations support the spot hypothesis for the cause of the variations observed in these stars.

Recent abundance determinations of B-type stars located in different parts of the Magellanic Clouds are presented and discussed.

Spectroscopic observations of 52 dK-dM stars, obtained at 640-665 nm (with spectral resolution 70-90 pm) using CCD detectors on the coude-feed telescope at KPNO since 1982, are reported. Data for four stars found to have diluted absorption or weak emission above continuum at H-alpha are presented in tables and spectra and discussed in detail. These objects (Gliese numbers 256, 425A, 900, and 907.1) are shown to be 'marginal' BY Dra stars, single objects of age 2.5-3 Gyr with activity and rotational velocity (3-5 km/s) between those of normal dM stars and those of true BY Dra stars. An explanation based on evolution from the BY Dra stage through marginal BY Dra to inactive dM is proposed.

The differential line shifts method for studying convective type motions has been described in the review of Glebocki and Stawikowski at this colloquium. Here the results of differential line shifts for twenty late type stars are presented. Line shifts were determined either from published wavelength measurements (α CMi, β Peg, α Boo, α Ser, α UMa, α Per, α Sco, γ Cyg α Car and HD 19445) or from my own wavelength measurements on 8.1 A/mm dispersion spectra (56 Ori, η Peg, η Psc, 61 Cyg A, e Eri, δ Eri, o Tau, e Cyg, α Aqr and ι Ari). Because of low accuracy of the wavelength determinations, mean shifts (VR) were calculated for narrow ranges of lower excitation potentials (LEP). These shifts were plotted against excitation potential and VR-LEP relations were obtained for all analysed stars. Because of the scatter of points in these diagrams linear approximation was assumed and the slopes (denoted A and expressed in Km/s/eV) of the VR-LEP relations were calculated. The stellar parameters and the derived slopes for the whole sample of investigated stars were analysed, and correlations with microturbulence, luminosity and gravity were found. These correlations demonstrate that the slope of VR-LEP relation describes some component of velocity field in late type stars. The detailed description of the procedure and results will be published in Acta Astronomica.

An account of the development of the study of stellar envelopes by means of maser lines is given.

High-resolution photographic spectra of the center of the solar disk have been obtained with the Vacuum Tower Telescope at Sacramento Peak Observatory. Two weak iron lines and the neighboring continuum were recorded with 40 sec tirae resolutions and better than i" spatial resolution over a period of 40 min. Intensity and velocity fluctuations were obtained in the two lines and continuum as a function of time and space, and 300 sec oscillations were filtered out. The resulting fluctuations, due solely to granulation, were assembled into an ensemble average of the center of a granule and the center of an intergranular lane, as a function of time. The intensity-fluctuation data have been analyzed through Calculation of model line profiles to yield temperature fluctuations in a granule as functions of time and height. We find that the line parameters are distinctly out of phase with continuum brightness, so that, for example, maximum brightness at line center occurs approximately, i00 sec prior to maximum continuum brightness. A series of one-dimensional model atmospheres representing the granule at various stages of its lifetime is presented. OBSERVED SOLAR SPECTRAL LINE ASYMMETRIES AND WAVELENGTH SHIFTS DUE TO CONVECTION Dainis Dravins Lund Observatory S-222 24 Lund, Sweden

After Haro’s fundamental discovery of flare stars in stellar associations and young clusters, their importance was fully recognized. The flare star system provides one of the most important records of the stellar aggregate’s history. This record can be used to establish the chronology of these systems and to test theories of star and aggregate formation. Unfortunately, the observational material contains an unavoidable strong selection with respect to the statistics and the physical characteristics of flare stars in aggregates. This explains the difficulties which arise when one tries to compare physical and statistical characteristics of flare stars in aggregates and in the solar neighborhood, since the latter objects are studied almost exclusively by photoelectric methods. The flare frequency in aggregates is more than one order of magnitude smaller than that of flare stars in the solar neighbourhood. This is probably a selection effect, since the photographic observations in aggregates have been carried out with exposure times 5-10 min. Small amplitude flares cannot be recorded at all. Flare stars in aggregates are usually objects whose recorded flares have amplitudes > 0 m .6 − 0 m .7, and which last for at least 5 min. The long exposure masks the true amplitude of the flare.

Les observations photometriques de l'etoile a rotation rapide TZ Tel sont presentees. Les courbes de lumiere sont analysees. La relation entre les variations des courbes de lumiere et les taches stellaires est etudiee. La rotation diffferentielle de TZ Tel est etablie

Un modele de melange turbulent, entre les couches H II ionisees et un vent stellaire chaud traverse par une onde de choc, considerant la turbulence conduite par une instabilite acoustique est developpe. Une application a la region H II NGC 6334 A est realisee

Because late-type stellar wind has low temperature, massive outflow, and high terminal velocity, theoretical models of thermal pressure or radiation pressure cannot explain the acceleration of late-type stellar wind. Energy damping of Alfven wave in stellar winds is small, and Alfven wave is perhaps the driving force of late-type stellar wind if the wave energy-flux is large enough. After theoretical analysis and numerical calculation, we get various velocity distributions by taking various wave energy-fluxes in reliable range, the terminal velocities accord with observations. If late-type stellar winds are driven by thermal pressure, the temperature is higher than acceptable. The results of Alfven wave driving winds also indicate that massive stellar winds need large energy flux and acceleration is closely related with gravity. In discussion we think that Alfven wave accelerating late-type stellar wind is feasible and the initial energy-flux, damping of Alfven wave in stellar winds need further study.

We investigate the near-ultraviolet high-resolution LWR spectra of the stars α Cas, β And, α Tau, β Gem, γ Cru, α Boo, and β Peg, obtained with the aid of the International Ultraviolet Explorer Satellite. We have given here a list of the strongest and most prevalent emission lines in the near-ultraviolet spectra of α Boo, KlIIIp, and β Peg, M2.5II-III which have the same luminosity class and different spectral type. The near-ultraviolet continuum flux measurements and integrated emission line fluxes of these stars for the 2500–3200 A region are presented in order to compare the variations in the appearance of the near-ultraviolet flux distribution with the temperature structure of their chromospheres for K and M giant stars. We also discuss differences between observed and calculated fluxes found from the Planck function.

The properties of the X-ray emission from normal stars, i.e., single stars located on the main-sequence or giant branch, are reviewed. Theoretical attempts to explain the observed X-ray emission both from early as well as late type stars are presented and, in particular, coronal length scale determination from spatially unresolved data is discussed and applied to the Sun as a star.

We observed the late-type stars Capella, σ2 CrB, λ And, AD Leo, GL494, GL569 and Procyon with different combinations of three instruments aboard EXOSAT : the low-energy channel multiplier array (LE), the medium-energy proportional counters (ME), and the transmission grating spectrometer (TGS). We derive crude temperature information on the coronae of these stars from the photometric data, using one- and two-temperature models of optically thin, thermal plasmas. We compare the results with 2-T fits and differential emission measure analyses of three grating observations and with simulations for mixtures of two plasma components with varying emission measure ratios. But for Procyon, all sources have a strong, hot component between 10 and 25 MK. The TGS spectra of Capella and σ2 CrB reveal a cooler component with comparable emission measure around 5 MK. The emission from the corona of Procyon is dominated by a very cool (0.6 MK) component, with an additional contribution from a 2–3 MK component.

We present deep 1.6 (H) and 2.2μm (K) images of the central parsec of the Galaxy at a resolution of 0.15″. We also give a brief history of high spatial resolution imaging of the Galactic Center in the near-infrared. Our recent speckle imaging results are: Most of the flux in earlier seeing limited images comes from about 340 unresolved stellar sources with K magnitudes