Wings Of Balmer Lines Research Articles

Search for flares and associated CMEs on late-type main-sequence stars in optical SDSS spectra

Aims.This work aims to detect and classify stellar flares and potential stellar coronal mass ejection (CME) signatures in optical spectra provided by the Sloan Digital Sky Survey (SDSS) data release 14. The sample is constrained to all F, G, K, and M main-sequence type stars, resulting in more than 630 000 stars. This work makes use of the individual spectral exposures provided by the SDSS.Methods.An automatic flare search was performed by detecting significant amplitude changes in theHαandHβspectral lines after a Gaussian profile was fit to the line core. CMEs were searched for by identifying asymmetries in the Balmer lines caused by the Doppler effect of plasma motions in the line of sight.Results.We identified 281 flares on late-type stars (spectral types K3 – M9). We identified six possible CME candidates showing excess flux in Balmer line wings. Flare energies inHαwere calculated and masses of the CME candidates were estimated. The derivedHαflare energies range from 3 × 1028− 2 × 1033erg. TheHαflare energy increases with earlier types, while the fraction of flaring times increases with later types. Mass estimates for the CME candidates are in the range of 6 × 1016− 6 × 1018g, and the highest projected velocities are ~300−700 km s−1.Conclusions.The low detection rate of CMEs we obtained agrees with previous studies, suggesting that for late-type main-sequence stars the CME occurrence rate that can be detected with optical spectroscopy is low.

Signatures of ubiquitous magnetic reconnection in the lower solar atmosphere

Ellerman Bomb-like brightenings of the hydrogen Balmer line wings in the quiet Sun, also known as quiet Sun Ellerman bombs (QSEBs), are a signature of the fundamental process of magnetic reconnection at the smallest observable scale in the lower solar atmosphere. We analyze high spatial resolution observations (0.″1) obtained with the Swedish 1-m Solar Telescope to explore signatures of QSEBs in the Hβ line. We find that QSEBs are ubiquitous and uniformly distributed throughout the quiet Sun, predominantly occurring in intergranular lanes. We find up to 120 QSEBs in the field of view for a single moment in time; this is more than an order of magnitude higher than the number of QSEBs found in earlier Hα observations. This suggests that about half a million QSEBs could be present in the lower solar atmosphere at any given time. The QSEB brightenings found in the Hβ line wings also persist in the line core with a temporal delay and spatial offset toward the nearest solar limb. Our results suggest that QSEBs emanate through magnetic reconnection along vertically extended current sheets in the lower solar atmosphere. The apparent omnipresence of small-scale magnetic reconnection may play an important role in the energy balance of the solar chromosphere.

Ultra metal-poor stars: improved atmospheric parameters and NLTE abundances of magnesium and calcium

Abstract The most metal-poor stars are the oldest objects, they provide a unique opportunity to study the earliest epoch of the Galaxy formation and individual nucleosynthesis events. These stars should be investigated with a scrupulous care, taking into account all available photometric, spectroscopic, and astrometric informations. We determined atmospheric parameters for 17 ultra metal-poor (UMP) stars, using an extensive method based on colour-Teff calibrations, isochrones, Gaia DR2 trigonometric parallaxes, and non-local thermodynamic equilibrium (NLTE) analysis of the Ca i/Ca ii ionization equilibrium and the Balmer line wings. We updated the model atom of Ca i- ii by including recent quantum-mechanical rate coefficients for the Ca i + H i and Ca ii + H i inelastic collisions. For any line of Ca i and Ca ii in our sample stars, the changes in collisional data result in a shift of smaller than 0.05 dex in the NLTE abundance. We determined magnesium and calcium NLTE and LTE abundances of our sample stars. For 10 stars, we found close-to-solar [Ca/Mg] NLTE abundance ratios. In the remaining stars, magnesium and calcium abundances do not follow each other, such that [Ca/Mg] varies between −3.15 and + 0.36, suggesting a contribution to stellar Mg and Ca abundances from a small number of supernova explosions with different properties. The obtained atmospheric parameters will be used in the forthcoming paper to determine NLTE abundances of chemical elements observed in spectra of the UMP stars.

Abundance analysis of the supergiant stars HD 80057 and HD 80404 based on their UVES Spectra

This study presents elemental abundances of the early A-type supergiant HD 80057 and the late A-type supergiant HD 80404. High resolution and high signal-to-noise ratio spectra published by the UVES Paranal Observatory Project (Bagnulo et al., 2003)11Based on data obtained with the UVES Paranal Observatory Project (ESO DDT Program ID 266.D-5655). were analyzed to compute their elemental abundances using ATLAS9 (Kurucz, 1993; 2005; Sbordone et al., 2004). In our analysis we assumed local thermodynamic equilibrium. The atmospheric parameters of HD 80057 used in this study are from Firnstein and Przybilla (2012), and that of HD 80404 are derived from spectral energy distribution, ionization equilibria of Cr i/ii and Fe i/ii, the fits to the wings of Balmer and Paschen lines as Teff = 7700 ± 150 K and log g = 1.60 ± 0.15 (in cgs). The microturbulent velocities of HD 80057 and HD 80404 have been determined as 4.3 ± 0.1 and 2.2 ± 0.0 km s−1, respectively. The rotational velocities are 15 ± 1 and 7 ± 2 km s−1 and their macroturbulence velocities are 24 ± 2 and 2 ± 1 km s−1. We have given the abundances of 25 ions of 19 elements for HD 80057 and 36 ions of 25 elements for HD 80404. The abundances are close to solar values, except for some elements (Na, Sc, Ti, V, Ba, and Sr). We have found the metallicities [M/H] for HD 80057 and HD 80404 as −0.16 ± 0.24 and −0.04 ± 0.16 dex, respectively. The evolutionary status of these stars are discussed and their nitrogen-to-carbon (N/C) and nitrogen-to-oxygen (N/O) ratios show that they are in their blue supergiant phase before the red supergiant region.

Impact of granulation effects on the use of Balmer lines as temperature indicators

Balmer lines serve as important indicators of stellar effective temperatures in late-type stellar spectra. One of their modelling uncertainties is the influence of convective flows on their shape. We aim to characterize the influence of convection on the wings of Balmer lines. We perform a differential comparison of synthetic Balmer line profiles obtained from 3D hydrodynamical model atmospheres and 1D hydrostatic standard ones. The model parameters are appropriate for F,G,K dwarf and subgiant stars of metallicity ranging from solar to 1/1000 solar. The shape of the Balmer lines predicted by 3D models can never be exactly reproduced by a 1D model, irrespective of its effective temperature. We introduce the concept of a 3D temperature correction, as the effective temperature difference between a 3D model and a 1D model which provides the closest match to the 3D profile. The temperature correction is different for the different members of the Balmer series and depends on the adopted mixing-length parameter in the 1D model. Among the investigated models, the 3D correction ranges from -300K to +300K. Horizontal temperature fluctuations tend to reduce the 3D correction. Accurate effective temperatures cannot be derived from the wings of Balmer lines, unless the effects of convection are properly accounted for. The 3D models offer a physically well justified way of doing so. The use of 1D models treating convection with the mixing-length theory do not appear to be suitable for this purpose. In particular, there are indications that it is not possible to determine a single value of the mixing-length parameter which will optimally reproduce the Balmer lines for any choice of atmospheric parameters.

Non-LTE Balmer line formation in late-type spectra: effects of atomic processes involving hydrogen atoms

Context.The wings of Balmer lines are often used as effective temperature diagnostics for late-type (F, G, K) stars under the assumption they form in local thermodynamic equilibrium (LTE).

Photometry and spectroscopy of CI camelpardalis from 1998–2005

Our long-time monitoring of the B[e] star and transient X-ray source CI Cam during quiescence following the 1998 outburst demonstrates that the complex, stratified circumstellar envelope has tended to stabilize after this structure was perturbed by the passage of a shock wave from the outburst. The star’s U BV R brightness shows slow, possibly cyclic, variations with an amplitude of about 0.2m. We determined the spectral type of the primary, B4III-V, based on the widths of the absorption wings of high-numbered Balmer lines. A Doppler shift of 460 km/s was detected for the Hell λ4686 A emission line. The shifts in this line yield an orbital period of 19.41 days, which is also manifested itself in the photometric data as a wave with a V amplitude of 0.034m. The orbit is elliptical, with an eccentricity of 0.62. It is most likely that the secondary is a white dwarf surrounded by an accretion disk. The primary’s mass exceeds 12 M ⊙ . The system may be at a late stage of its evolution, after the stage of mass exchange.

Stellar and wind parameters of Galactic O-stars

We have re-analyzed the Galactic O-star sample from Puls et al. (1996) by means of line-blanketed NLTE model atmospheres in order to investigate the influence of line-blocking/blanketing on the derived parameters. The analysis has been carried out by fitting the photospheric and wind lines from H and He. In most cases we obtained a good fit, but we have also found certain inconsistencies which are probably related to a still inadequate treatment of the wind structure. These inconsistencies comprise the line cores of H γ and H β in supergiants (the synthetic profiles are too weak when the mass-loss rate is determined by matching H α ) and the generalized dilution effect (cf. Voels et al. 1989) which is still present in He I 4471 of cooler supergiants and giants. Compared to pure H/He plane-parallel models we found a decrease in effective temperatures which is largest at earliest spectral types and for supergiants (with a maximum shift of roughly 8000 K). This finding is explained by the fact that line-blanketed models of hot stars have photospheric He ionization fractions similar to those from unblanketed models at higher T eff and higher log g. Consequently, any line-blanketed analysis based on the He ionization equilibrium results in lower T eff -values along with a reduction of either log g or helium abundance (if the reduction of log g is prohibited by the Balmer line wings). Stellar radii and mass-loss rates, on the other hand, remain more or less unaffected by line-blanketing. We have calculated new spectroscopic masses and compared them with previous results. Although the former mass discrepancy (Herrero et al. 1992) becomes significantly reduced, a systematic trend for masses below 50 M ○. seems to remain: The spectroscopically derived values are smaller than the evolutionary masses by roughly 10 M ○. . Additionally, a significant fraction of our sample stars stays over-abundant in He, although the actual values were found to be lower than previously determined. Also the wind-momentum luminosity relation (WLR) changes because of lower luminosities and almost unmodified wind-momentum rates. Compared to previous results, the separation of the WLR as a function of luminosity class is still present but now the WLR for giants/dwarfs is consistent with theoretical predictions. We argue that the derived mass-loss rates of stars with H α in emission are affected by clumping in the lower wind region. If the predictions from different and independent theoretical simulations (Vink et al. 2000; Pauldrach et al. 2003; Puls et al. 2003a) that the WLR should be independent of luminosity class were correct, a typical clumping factor / 2 5 should be derived by unifying the different WLRs.

Quantitative Spectroscopy of Supergiants

Blue supergiants of spectral types B and A are the visually brightest stars in spiral and irregular galaxies, with their most luminous members (at ) outshining entire dwarf galM 10 V axies. This characteristic allows us to use them as probes to study the local universe in great detail. In principle, already existing large telescopes and instrumentation facilitate quantitative spectroscopy of these objects as far as the Virgo and Fornax clusters of galaxies. Beyond their challenging stellar atmospheres and opportunities for testing sophisticated nonLTE physics, they offer numerous applications to modern astrophysics. Quantitative spectroscopy of supergiants will contribute to improving our understanding of massive-star evolution. Galactic abundance gradients and abundance patterns, as will be obtained from studies of large ensembles of supergiants in our own and other galaxies, will foster the understanding of galactochemical evolution. Finally, they are promising independent indicators for calibrating the extragalactic distance scale, by application of the wind momentum–luminosity and the flux-weighted gravity–luminosity relationships (R. P. Kudritzki et al. 1999, AA R. P. Kudritzki, F. Bresolin, & N. Przybilla 2003, ApJ, 582, L83). In view of this large potential, the objective of this thesis is to improve the status of quantitative spectroscopy of BA-type supergiants and to provide first applications on a sample of Galactic and extragalactic targets. It is shown that among the model atmospheres available at present, the best suited for analyses of supergiants are line-blanketed classical LTE models. An investigation of the impact of various parameters such as helium abundance and line blanketing on the atmospheric structure shows that for the most luminous objects, an accurate treatment of these parameters is essential for a quantitative analysis, whereas the less luminous supergiants react less sensitively. Spectrum synthesis is used to model the line spectra. It is the only technique capable of providing analyses of spectra of different qualities from low to high resolution and able to cope with heavy line blending at a broad range of signal-tonoise ratios. The stellar parameters are determined from purely spectroscopic indicators, from temperatureand gravity-sensitive ionization equilibria and the Balmer line wings. Elemental abundances are derived by modeling individual spectral features. Several tens of thousands spectral lines from 28 chemical species are included in the line formation, allowing almost the entire observed spectra to be reproduced. Non-LTE effects become important in blue supergiants, where a strong radiation field at low particle densities favors deviations from LTE. Comprehensive model atoms are therefore constructed for C i/ii, N i/ii, O i, and Mg i/ii in order to determine non-LTE level populations (N. Przybilla, K. Butler, & R. P. Kudritzki 2001, AA N. Przybilla & K. Butler 2001, AA N. Przybilla et al. 2000, AA N. Przybilla et al. 2001, A&A, 369, 1009). Highly accurate radiative and collisional atomic data recently determined for astrophysical and fusion research using the R-matrix method in the closecoupling approximation are incorporated. In addition, model atoms for H, He i, O ii, S ii/iii, Ti ii, and Fe ii are adopted from the literature, the atomic data being updated to more modern values in some cases. Thus, an improved treatment for the main elements of astrophysical interest is achieved. Extensive testing of the atomic data is performed for the nearby bright main-sequence standard Vega (A0 V), at welldetermined stellar parameters and atmospheric structure. A high-resolution and low-noise spectrum with large wavelength coverage from the visual to the near-IR is used for this purpose. Further tests are performed for the Galactic supergiants h Leo, HD 111613, HD 92207, and b Ori, with similar high-quality spectra in order to study the non-LTE effects across the parameter space. Accurate and consistent stellar parameters are derived for these. Non-LTE ionization equilibria of several elements—typically N i/ii, O i/ii, Mg i/ii, and S ii/iii—agree simultaneously, provided that a realistic treatment of line blocking is used. These parameters also constitute important input data for further studies of the stellar winds of these objects. Accounting for non-LTE reduces the random errors and removes systematic trends in the analyses. In particular, the improved treatment of electron collisions largely removes longstanding discrepancies in analyses of lines from different spin systems of a given ion. The computed non-LTE line profiles fit the observations well for the different species at a given elemental abundance. In the parameter range covered, all lines from He i, C i/ii, N i/ii, O i/ii, and S ii/iii are significantly

Differential O and Si Abundances in M33 Early B Supergiants

We present non-LTE analyses of four M33 early B-supergiant stars and five Galactic counterparts. This is the first time that B supergiants beyond the Magellanic Clouds are analyzed by means of detailed Non-LTE techniques. Stellar temperatures, gravities, microturbulences and Si abundances are derived for all objects using the Si ionization equilibrium and the Balmer line wings. O abundances are then also derived. Important approximations made during the calculations are described, and their influence on the results is analyzed. It is found that these approximations have no significant effect on the results at any microturbulence. We find that a strict differential analysis is needed to detect abundance differences. Thus we compare results line by line in M33 and Galactic stars of stellar parameters as similar as possible. Three of the four M33 stars turned out to be O deficient as compared to their Galactic counterparts, and only one, close to the center of M33 (M33 1054) is found to be moderately O enriched. From these differential analyses we find that our data are compatible with a radial O gradient in M33 as that derived from HII region data: we obtain -0.19+/-0.13 or -0.20+/-0.07 dex/kpc, depending on whether B133 is included or not. Our data are also consistent with other possibilities such as a steep increase of the O abundance in the inner region (at projected distances less than 9 arcmin from the center of M33), followed by a flat O abundance profile towards the outer parts of M33. Si shows the same pattern, and it is shown that Si and O correlate well, as expected for alpha-elements, supporting then the high value of the O abundance gradient in M33 as compared to the Milky Way and other nearby spiral galaxies.

Time-dependent Flare Signature in Hydrogen Balmer Lines

In recent studies of Hα flare imaging spectroscopy performed by Leka et al. and de la Beaujardière et al. in 1993, Hα line profiles have been investigated as a function of space to locate the physical process underlying observed spectral profiles. In this Letter, we discuss time evolution of hydrogen Balmer line profiles at a fixed spatial point recorded by the multichannel spectrograph at Nanjing University in China during the 1991 October 27 white-light flare which occurred in NOAA 6891. It is found that the Balmer emission lines with a central reversal show up at the beginning of the Hα flare but change to single-peaked profiles in about 30 s. This result may, according to Canfield et al.'s model in 1993, indicate that the Balmer line enhancement even at one flare site could be caused by two physical processes, namely, initially by the high-energy particle precipitation and subsequently by the high coronal pressure. We also present evidence for downward motion and the Stark broadening effect on the observed Balmer line wings to examine further the physical consequences of the particle precipitation. Time correlation of the Balmer line emission with hard X-ray and continuum brightening is briefly discussed based on the spectral information.

THE TEMPERATURES OF F-K DWARFS AND THE SOLAR VALUE OF R-I

ABSTRACT From published FGK-star data, the solar value of (R-I)c is found to be 0.337 ± 0.0024 mag. The equivalent value of (R-I)J is 0.343 ± 0.0033 mag. The data base which yields these values includes integrated Halpha and Hbeta measurements and also temperatures derived from Balmer-line wings. These latter temperatures can be combined with the quoted value of (R-I)c and data from the infrared flux method to yield a temperature calibration. The result is theta=1.075(R-I)c + 0510, and is valid for F III-V, G IV-V, and K V stars with 0.06.

Inferring chromospheric flare heating from hydrogen-line wings

Strong flare heating that penetrates deeply into the solar chromosphere is examined, and a simple model that is supported by a numerical radiative transfer simulation is applied to study how elevated free electron densities produce markedly increased Stark emission in the wings of hydrogen Lyman and Balmer lines. The proportionality that exists between the observed Stark wing intensity and the total energy deposition in the partially ionized layer is calculated for various Lyman and Balmer lines. It is concluded that when the effects of background opacity sources on the wing enhancements are not important, the magnitude of the nonthermal heating that penetrates the chromosphere may be inferred from the observed line wings. It is predicted that Ly-alpha extended wings will exhibit enhancement of Stark shape, even when inherent damping wing opacity exceeds Stark wing opacity over the entire absorption profile.

A study of the eclipsing cataclysmic variable Lanning 90

Photometric and spectroscopic observations of Lanning 90 (V1776 Cyg) show that it is an eclipsing cataclysmic variable with an orbital period of 3h57m. The shape of the eclipse is variable, and the brightness out of eclipse can change by over a magnitude in less than a day. The broad-band light curves do not show a hump before eclipse, but time-resolved spectroscopy of one orbit suggests that the H-alpha emission-line strength peaks near phase 0.75. Observations of a number of orbits, however, are needed to confirm that the line strength depends on phase. The velocity amplitude of the primary is 144 + or - 20 km/s as measured from the wings of the H-alpha line. The masses of the components, the orbital inclination, and semimajor axis are estimated from the observations, but the derived system parameters are suspect since the spectroscopic phase lags the photometric phase by 70 deg. A similar shift has been observed in DW UMa and is attributed to a disturbance on the disk which contaminates the Balmer line wings. 20 refs.

On the interpretation of emission wings of balmer lines in LBV’s

The optical spectra of Luminous Blue Variables (LBV’s) are characterized by strong Balraer emission lines. In many cases, the narrow emission component (FWHM ≤ 300 km/sec) shows extended emission wings reaching up to -1000 km/sec. These wings are generally attributed to electron scattering of line photons in the dense stellar wind (Bernat and Lambert 1978). In this paper we discuss an alternative mechanism which may partly contribute to the observed line wings.

FUV and optical spectrophotometry of X-ray selected Seyferts

Nearly simultaneous FUV and optical spectrophotometry of X-ray selected Seyfert galaxies has revealed an average Ly α/H β ratio of 22, a positive correlation between the ratio Ly α/H β and the width of the lines, and additional Ly α emission in the wings of one source which is not matched by emission in the Balmer line wings. However, we find no distinguishing features in the continuum emission from these X-ray selected objects compared with other samples. If the correlation between Ly α/H β and the width of the lines is found to apply to larger samples of Seyferts, it may be that our objects appear Ly α bright because they are also broad-lined compared with other samples.

The dwarf nova Z Chamaeleontis - II. Spectroscopy

Spectroscopic observations of Z Cha in quiescence are presented. The data include moderate spectral resolution scans over most of an orbit and with high time resolution through eclipse. Various lower resolution spectra and UV and optical spectrophotometry are also discussed. The spectrum is dominated by broad double peaked Balmer emission lines; He I emission and absorption lines are visible and there is no Balmer discontinuity. The Balmer line wings extend to ± 2100 km s−1; this implies a miminum mass |$M_\text{WD} \gt 0.4M_\odot$| if the compact object is a helium white dwarf. The depth of the central dip in the double peaked profiles and the peak-to-peak velocity separation increase from Hα through to Hδ suggesting absorption effects. The values of the peak-to-peak velocity separation range from 1100 km s−1 (Hα) to 1650 km s−1 (Hδ). The line emissivity as a function of disc radius is discussed and power-law fits given. The Balmer line fluxes do not vary very much with orbital phase. The Balmer decrement is fairly flat and is consistent with densities |$N_\text e \sim 10^{8-16}\text{cm}^{-3}$|⁠. Assuming the Balmer emission lines originate in the disc, the eclipse shows that the disc rotates in the same sense as the orbit and is consistent with (but does not show) the inside of the disc rotating faster than the outside. Radial velocity measurements give limits on the velocity of the centre of the emission line region as |$50\lt K_\text{em}\enspace(\text{km}\enspace \text s ^{-1})\lt 200$|⁠. The UV and optical continua do not join up consistently. The UV continuum is weak and is consistent with a disc. The optical continuum and the reddening during eclipse suggest the presence of a red star and/or disc outer edge which is expected to dominate the spectrum between 1–2 µm.

Spectroscopic study of the eclipsing binary V 367 Cygni

Seventeen coude spectrograms (dispersion 20 A mm−1) of the β Lyrae-type eclipsing binary V 367 Cygni (P=18.6 d) have been studied. The observations were made at the Haute Provence Observatory during a period of almost two years (May 1973–March 1975). An anomalous behavior for the radial velocities of the spectrograms taken during one cycle (406) was observed; it is suggested that gas eruption under form of prominences may explain it. The spectrum is dominated by shell lines very similar to those present in the spectrum of the supergiant A9 Ia e Aurigae. The underlying stellar spectrum is classified as A5 I on the basis of the intensity of the sole clearly visible stellar line, λ4481 MgII, of the wings of the stellar Balmer lines, and an estimate of the intensity of the stellarK line. The radial velocity curves for the shell lines of CaII, HI, metallic ions and neutral iron, as well as the phase dependence of the microturbulence, indicate stratification in the shell.

Photoelectric Magnetic Field Measurements of Ap and Bp Stars

SummaryMagnetic field measurements of numerous Ap and Bp stars have been obtained using a photoelectric technique similar to that employed in the solar magnetograph, applied to Balmer line wings. The accuracy of field measurements obtained is almost independent of projected rotation velocity. A survey of rapidly rotating (v. sin i ≥ 30 km/sec) Ap stars shows that fields of more than 1 kgauss are significantly less common among rapidly rotating Ap stars than among slowly rotating ones. Magnetic fields have been found in two rapidly rotating Ap stars, four southern Ap stars, and the helium-weak star 3 Sco. Magnetic curves obtained for the known magnetic stars 53 Cam and α2CVn show significant differences from the curves observed photographically, in ways which can alter conclusions drawn about the field distributions over the surface of these stars.

New Observations of the Optical Spectrum of the Seyfert Galaxy NGC 4151

Spectra and scans of NGC 4151 are found to show broad lines of He I and Fe II. The He I lines are twice the width of the Balmer line wings and the broad line spectrum closely resembles that of 3C 273 Limits to the density and temperature for the region emitting the broad lines are deduced. The narrow forbidden lines are emitted in a region with log T = 4·07 ± 0·03 and density (possibly stratified) between log Ne ~ 4·3 and 3·7. How the hydrogen and helium line widths can differ is briefly discussed. Possible reasons for the difference between quasars and Seyferts with Fe II emission and those with strong forbidden line spectra are advanced.