Balmer Line Profiles Research Articles

Abundance analysis of HD 22920 spectra

AbstractThe new spectropolarimetric observations of HD 22920 with ESPaDOnS at CFHT reveal a strong variability of its spectral line profiles with the phase of stellar rotation. We have obtained Teff = 13640 K, logg=3.72 for this star from the best fit of its nine Balmer line profiles. The respective model of stellar atmosphere was calculated to perform abundance analysis of HD 22920 using the spectra obtained for three different phases of stellar rotation. We have found that silicon and chromium abundances appear to be vertically stratified in the atmosphere of HD 22920. Meanwhile, silicon shows hints for a possible variability of vertical abundance stratification with rotational phase.

Project VeSElkA : Preliminary results for CP stars recently observed with ESPaDOnS

AbstractWe present the first results for the estimation of gravity and effective temperature of poorly studied chemically peculiar stars recently observed with the spectropolarimeter ESPaDOnS at CFHT in the frame of the VeSElkA (Vertical Stratification of Elements Abundance) project. A grid of theoretical stellar atmosphere models with the corresponding fluxes has been calculated using the PHOENIX code. We have used these fluxes to fit Balmer line profiles employing the code FITSB2 that produces estimates of the effective temperature, surface gravity and radial velocity for each star.

Hour-timescale profile variations in the broad Balmer lines of the Seyfert galaxy Hour-timescale profile variations in the broad Balmer lines of the Seyfert galaxy Markarian 6

AbstractPart of results of the multi-epoch intranight optical spectroscopic monitoring of the Markarian 6 nucleus carried out at the telescopes of 6-m of the Special Astrophysical Observatory (Russia), 2.6-m of the Byurakan Astrophysical Observatory (Armenia) and 2-m of the Tautenburg Observatory (Germany) is presented.Observations were made in 1979, 1986, 1988-1991 and 2007-2009 during a total of 33 nights with an average sampling rate of 4 spectra per night. TV-scanner and long-slit spectrographs equipped with Image Tube and CCD detector arrays were used. Altogether we analyzed 110 Hβ and 58 Hα region spectra to search for intranight variability in the broad hydrogen emission line profiles. The typical spectral resolutions were 4 Å for scanner spectra, 6 Å for photographic spectra, and 5 Å and 10 Å for CCD spectra. The S/N ratio at the continuum level near the Hβ and Hα lines was in the range 15–50.The purpose of the search was to look for the characteristic variability signatures of different kinematical models of the broad emission-line region. We considered the centering and guiding errors which can result in differences between spectra.We found variations in the broad Balmer line difference profiles on time scale of hour with the level of significance of 3.6 σ to 5.0 σ. Variations take the form of narrow, small bumps located at the blue and red sides or only at the blue side of the lines. In the intermediate level of broad line flux, the Hβ and Hα profiles show fine structure. Detected profile changes occurred at the same radial velocity shifts as the details in the fine structure.The variability is at least 2 orders of magnitude more rapid than any observed for broad Balmer line profiles in AGNs that we are aware of in the literature.Discovered extremely rapid line-profile variability may be associated with reverberation effects. Two-sided profile changes may indicate the response of circularly rotating hydrogen clouds in the BLR to a light pulse from a central source. One-sided profile variations may be attributed to a response of a non-disk component: the subarcsec scale region of the jet.

Energy distributions of neutrals and charged species in hollow cathode H2 discharges: a study of fast H atoms

A joint study of atomic and molecular emission spectroscopy, ion mass spectrometry and Langmuir probes is presented for a hollow cathode H2 discharge at pressures 0.7–20 Pa, rendering energy distributions of the different groups of particles that span five orders of magnitude. The H Balmer line profiles can be decomposed into three contributions (‘narrow peak’, ‘plateau’ and ‘far wings’) with very different widths. The narrow peak and the plateau are largely attributed to electron impact dissociative excitation and ionization of H2, and display Doppler temperatures of ∼0.3 eV and ∼6 eV, respectively. The energy-resolved mass spectra of H+ confirm the assignment of the plateau region. The far wings give rise to emissions extending to Doppler shifts of 0.5 nm, which correspond to translational energies of ∼300 eV. The dependence of the relative intensities of these components on pressure is studied. With a grounded grid before the observation window, a structure is induced in the blue-shifted wing. Assuming that the structure is solely caused by dissociative excitation of H2 upon collisions with the plasma ions (H+, and ), their relative concentrations can be estimated. These estimations are in very good agreement with the values derived from independent mass spectrometric measurements.

Hydrogen transport diagnostics by atomic and molecular emission line profiles simultaneously measured for large helical device

We observe the Balmer-α, -β, and -γ lines of hydrogen atoms and Q branches of the Fulcher-α band of hydrogen molecules simultaneously with their polarization resolved for large helical device. From the fit including the line splits and the polarization dependences by the Zeeman effect, the emission locations, intensities, and the temperatures of the atoms and molecules are determined. The emission locations of the hydrogen atoms are determined outside but close to the last closed flux surface (LCFS). The results are consistent with a previous work (Phys. Plasmas 12, 042501 (2005)). On the other hand, the emission locations of the molecules are determined to be in the divertor legs, which is farer from those of the atoms. The kinetic energy of the atoms is 1 ∼ 20 eV, while the rotational temperature of molecules is ∼0.04 eV. Additionally, substantial wings, which originate from high velocity atoms and are not reproduced by the conventional spectral analysis, are observed in the Balmer line profiles. We develop a one-dimensional model to simulate the transport of the atoms and molecules. The model reproduces the differences of the emission locations of the atoms and molecules when their initial temperatures are assumed to be 3 eV and 0.04 eV, respectively. From the model, the wings of the Balmer-α line is attributed to the high velocity atoms exist deep inside the LCFS, which are generated by the charge exchange collisions with hot protons there.

The cold veil of the Milky Way stellar halo

We build a sample of distant (D > 80 kpc) stellar halo stars with measured radial velocities. Faint ($20 < g <22$) candidate blue horizontal branch (BHB) stars were selected using the deep, but wide, multi-epoch Sloan Digital Sky Survey photometry. Follow-up spectroscopy for these A-type stars was performed using the VLT-FORS2 instrument. We classify stars according to their Balmer line profiles, and find 7 are bona fide BHB stars and 31 are blue stragglers (BS). Owing to the magnitude range of our sample, even the intrinsically fainter BS stars can reach out to D ~ 90 kpc. We complement this sample of A-type stars with intrinsically brighter, intermediate-age, asymptotic giant branch stars. A set of 4 distant cool carbon stars is compiled from the literature and we perform spectroscopic follow-up on a further 4 N-type carbon stars using the WHT-ISIS instrument. Altogether, this provides us with the largest sample to date of individual star tracers out to r ~ 150 kpc. We find that the radial velocity dispersion of these tracers falls rapidly at large distances and is surprisingly cold (sigma_r ~ 50-60 km/s) between 100-150 kpc. Relating the measured radial velocities to the mass of the Milky Way requires knowledge of the (unknown) tracer density profile and anisotropy at these distances. Nonetheless, by assuming the stellar halo stars between 50-150 kpc have a moderate density fall-off (with power-law slope alpha < 5) and are on radial orbits (sigma^2_t/sigma^2_r < 1), we infer that the mass within 150 kpc is less than 10^12 M_solar and suggest it probably lies in the range (5-10) x 10^11 M_solar. We discuss the implications of such a low mass for the Milky Way.

TOTAL AND GAS FLOW ACTIVITY OF THE SEYFERT GALAXY NGC3227 NUCLEUS FOR ITS DIFFERENT EVOLUTIONARY EPOCHS

A comparative analysis of time variations of spectral characteristics of the Seyfert galaxy NGC 3227 nucleus: equivalent widths (EW λ), relative intensities, the width of the Balmer line profiles was carried out. Spectral data obtained in April 2009 with the 1.5-m Russian-Turkish telescope (RTT-150) and data published in the literature were used. Results of the comparative analysis showed the weakening of total activity and, consequently, gas flow activity of the galaxy nucleus in the time interval of more than 30 years.

The VLT-FLAMES survey of massive stars: Nitrogen abundances for Be-type stars in the Magellanic Clouds

Aims. We compare the predictions of evolutionary models for early-type stars with atmospheric parameters, projected rotational velocities and nitrogen abundances estimated for a sample of Be-type stars. Our targets are located in 4 fields centred on the Large Magellanic Cloud cluster: NGC 2004 and the N 11 region as well as the Small Magellanic Cloud clusters: NGC 330 and NGC 346. Methods. Atmospheric parameters and photospheric abundances have been determined using the non-LTE atmosphere code tlusty. Effective temperature estimates were deduced using three different methodologies depending on the spectral features observed; in general they were found to yield consistent estimates. Gravities were deduced from Balmer line profiles and microturbulences from the Si iii spectrum. Additionally the contributions of continuum emission from circumstellar discs were estimated. Given its importance in constraining stellar evolutionary models, nitrogen abundances (or upper limits) were deduced for all the stars analysed. Results. Our nitrogen abundances are inconsistent with those predicted for targets spending most of their main sequence life rotating near to the critical velocity. This is consistent with the results we obtain from modelling the inferred rotational velocity distribution of our sample and of other investigators. We consider a number of possibilities to explain the nitrogen abundances and rotational velocities of our Be-type sample.

A SPECTROSCOPIC SURVEY AND ANALYSIS OF BRIGHT, HYDROGEN-RICH WHITE DWARFS

We have conducted a spectroscopic survey of over 1300 bright (V < 17.5), hydrogen-rich white dwarfs based largely on the last published version of the McCook & Sion catalog. The complete results from our survey, including the spectroscopic analysis of over 1100 DA white dwarfs, are presented. High signal-to-noise ratio optical spectra were obtained for each star and were subsequently analyzed using our standard spectroscopic technique where the observed Balmer line profiles are compared to synthetic spectra computed from the latest generation of model atmospheres appropriate for these stars. First, we present the spectroscopic content of our sample, which includes many misclassifications as well as several DAB, DAZ, and magnetic white dwarfs. Next, we look at how the new Stark broadening profiles affect the determination of the atmospheric parameters. When necessary, specific models and analysis techniques are used to derive the most accurate atmospheric parameters possible. In particular, we employ M dwarf templates to obtain better estimates of the atmospheric parameters for those white dwarfs that are in DA+dM binary systems. Certain unique white dwarfs and double-degenerate binary systems are also analyzed in greater detail. We then examine the global properties of our sample including the mass distribution and their distribution as a function of temperature. We then proceed to test the accuracy and robustness of our method by comparing our results to those of other surveys such as SPY and SDSS. Finally, we revisit the ZZ Ceti instability strip and examine how the determination of its empirical boundaries are affected by the latest line profile calculations.

STRONG RESPONSE OF THE VERY BROAD Hβ EMISSION LINE IN THE LUMINOUS RADIO-QUIET QUASAR PG 1416-129

We report new spectroscopic observations performed in 2010 and 2011 for luminous radio-quite quasar PG 1416-129. Our new spectra with high quality cover both H$\beta$ and H$\alpha$ regions, and show negligible line profile variation within a timescale of one year. The two spectra allow us to study the variability of the Balmer line profile by comparing the spectra with the previous ones taken at 10 and 20 years ago. By decomposing the broad Balmer emission lines into two Gaussian profiles, our spectral analysis suggests a strong response to the continuum level for the very broad component, and significant variations in both bulk blueshift velocity/FWHM and flux for the broad component. The new observations additionally indicate flat Balmer decrements (i.e., too strong H$\beta$ emission) at the line wings, which is hard to be reproduced by recent optically thin models. With these observations we argue that a separate inner optically thin emission-line region might not be necessary in the object to reproduce the observed line profiles.

The accuracy of stellar atmospheric parameter determinations: a case study with HD 32115 and HD 37594★

We present detailed parameter determinations of two chemically normal late A-type stars, HD 32115 and HD 37594, to uncover the reasons behind large discrepancies between two previous analyses of these stars performed with a semi-automatic procedure and a "classical" analysis. Our study is based on high resolution, high signal-to-noise spectra obtained at the McDonald Observatory. Our method is based on the simultaneous use of all available observables: multicolor photometry, pressure-sensitive magnesium lines, metallic lines and Balmer line profiles. Our final set of fundamental parameters fits, within the error bars, all available observables. It differs from the published results obtained with a semi-automatic procedure. A direct comparison between our new observational material and the spectra previously used by other authors shows that the quality of the data is not the origin of the discrepancies. As the two stars require a substantial macroturbulence velocity to fit the line profiles, we concluded that neglecting this additional broadening in the semi-automatic analysis is one origin of discrepancy. The use of FeI excitation equilibrium and of the Fe ionisation equilibrium, to derive effective temperature and surface gravity, respectively, neglecting all other indicators leads to a systematically erroneously high effective temperature. We deduce that the results obtained using only one parameter indicator might be biased and that those results need to be cautiously taken when performing further detailed analyses, such as modelling of the asteroseismic frequencies or characterising transiting exoplanets.

The cool magnetic DAZ white dwarf NLTT 10480

We have identified a new, cool magnetic white dwarf in the New Luyten Two-Tenths (NLTT) catalogue. The high proper-motion star NLTT 10480 (mu=0.5"/year) shows weak Zeeman-split lines of calcium, as well as characteristic Halpha and beta Zeeman triplets. Using VLT X-shooter spectra we measured a surface-averaged magnetic field B_S ~ 0.5 MG. The relative intensity of the pi and sigma components of the calcium and hydrogen lines imply a high inclination (i > 60 deg). The optical-to-infrared V-J colour index and the CaI/CaII ionization balance indicate a temperature between 4900 and 5200 K, while the Balmer line profiles favour a higher temperature of 5400 K. The discrepancy is potentially resolved by increasing the metallicity to 0.03x solar, hence increasing the electron pressure. However, the measured calcium abundance and abundance upper limits for other elements (Na, Al, Si. and Fe) imply a low photospheric metallicity < 10^{-4} solar. Assuming diffusion steady-state, a calcium accretion rate of log(dM/dt)(g/s)=5.6+/-0.3 is required to sustain a calcium abundance of log(n(Ca)/n(H))=-10.30+/-0.30 in the white dwarf atmosphere. We examine the implications of this discovery for the incidence of planetary debris and weak magnetic fields in cool white dwarf stars.

On the sdOB primary of the post common-envelope binary AA Doradus (LB 3459)

AA Dor is an eclipsing, post common-envelope binary with an sdOB-type primary and a low-mass secondary. Eleven years ago, an NLTE spectral analysis showed a discrepancy in the surface gravity that was derived by radial-velocity and light-curve analysis, log g = 5.21 +/- 0.1 (cm/sec^2) and log g = 5.53 +/- 0.03, respectively. We aim to determine both the effective temperature and surface gravity of AA Dor precisely from high-resolution, high-S/N observations taken during the occultation of the secondary. We calculated an extended grid of metal-line blanketed, state-of-the-art, non-LTE model atmospheres in the parameter range of the primary of AA Dor. Synthetic spectra calculated from this grid were compared to optical observations. We verify Teff = 42000 +/- 1000 K from our former analyses and determine a higher log g = 5.46 +/- 0.05. The main reason are new Stark-broadening tables that were used for calculating of the theoretical Balmer-line profiles. Our result for the surface gravity agrees with the value from light-curve analysis within the error limits, thereby solving the so-called gravity problem in AA Dor.

The HαBalmer line as an effective temperature criterion

Aims. We attempt to derive the true effective temperature of a star from the spectroscopic observation of its Hα Balmer line profile. Methods. The method is possible thanks to advances in two respects. First there have been progresses in the theoretical treatment of the broadening mechanisms of Hα. Second, there has been a rapid increase in the number of stars with an apparent diameter measured with an accuracy of the order of 1 percent, enabling us to obtain an accurate effective temperature Teff for a dozen of stars using the direct method by means of combining the apparent diameter and the bolometric flux. Results. For the eleven stars with an accurate effective temperature derived from their apparent angular diameter we determined the effective temperature of the Kurucz Atlas9 model that provides the best fit of the computed theoretical Hα profile (using the recent theoretical advances) with the corresponding observed profile, extracted from the S4N spectroscopic database. The two sets of effective temperatures have a significant offset, but are tightly correlated, with a correlation coefficient of 0.9976. The regression straight line of Teff(direct) versus Teff(Hα) enables us to reach the true effective temperature from the spectroscopic observation of the Hα profile, with an rms error of only 30 K. This provides a way of obtaining the true effective temperature of a reddened star. Conclusions. We succeeded in obtaining empirically the true stellar effective temperature from Hα profile using Kurucz’s Atlas9 grid of 1D model atmospheres. Full understanding of the difference between Teff(direct) and Teff(Hα) would require a 3D approach, with radiative hydrodynamical models, which will be the subject of a future paper.

Modeling of Solar Flare Plasma and Its Radiation

We present a modular and highly versatile test particle-radiative hydrodynamic code which simultaneously models the particle beam energy transport and deposition, the corresponding explosive response of the flare atmosphere and the NLTE (NLTE, plasma and radiation out of the local thermodynamic equilibrium) radiative transfer for partly ionized hydrogen in the chromosphere and photosphere. The computational domain covers the photosphere, the chromosphere, the transition region, and the corona with the initial hydrostatic preflare atmosphere. To demonstrate the potential of the code, we calculate the time evolution of the Balmer line profiles corresponding to the time variation of the electron beam flux derived from the observed flare hard X-ray emission.

Optical spectroscopy of DPVs and the case of LP Ara

AbstractWe present preliminary results of our spectroscopic campaign of a group of intermediate mass interacting binaries dubbed “Double Periodic Variables” (DPVs), characterized by orbital light curves and additional long photometric cycles recurring roughly after 33 orbital periods (Mennickent et al. 2003, 2005). They have been interpreted as interacting, semi-detached binaries showing cycles of mass loss into the interstellar medium (Mennickent et al. 2008, Mennickent &amp; Kołaczkowski 2009). High resolution Balmer and helium line profiles of DPVs can be interpreted in terms of mass flows in these systems. A system solution is given for LP Ara, based on modeling of the ASAS V-band orbital light curve and the radial velocity of the donor star.

The double degenerate system NLTT 11748

We show that the extremely low-mass white dwarf NLTT 11748 (0.17 ) is in a close binary with a fainter companion. We obtained a series of radial velocity measurements of the low-mass white dwarf using the H<i>α<i/> core and determined an orbital period of <i>5.64<i/> h. The velocity semi-amplitude (<i>K<i/> = 274.8 km s<sup>-1<sup/>) and orbital period imply that it is a degenerate star, and that the minimum mass for the companion is 0.75 (assuming a mass of 0.167 for the primary). Our analysis of Balmer line profiles shows that a 0.75 white dwarf companion does not contribute more than 2% or 5% of the flux (<i>V<i/>-band) for helium- or hydrogen-rich surfaces, respectively. The kinematics of the system suggest that it belongs to the Galactic halo.

THE LICK AGN MONITORING PROJECT: REVERBERATION MAPPING OF OPTICAL HYDROGEN AND HELIUM RECOMBINATION LINES

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7M_sun and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hbeta emission, which we have previously reported. We present here the light curves for the Halpha, Hgamma, HeII 4686, and HeI 5876 emission lines and the time lags for the emission-line responses relative to changes in the continuum flux. Combining each emission-line time lag with the measured width of the line in the variable part of the spectrum, we determine a virial mass of the central supermassive black hole from several independent emission lines. We find that the masses are generally consistent within the uncertainties. The time-lag response as a function of velocity across the Balmer line profiles is examined for six of the AGNs. Finally we compare several trends seen in the dataset against the predictions from photoionization calculations as presented by Korista & Goad. We confirm several of their predictions, including an increase in responsivity and a decrease in the mean time lag as the excitation and ionization level for the species increases. Further confirmation of photoionization predictions for broad-line gas behavior will require additional monitoring programs for these AGNs while they are in different luminosity states. [abridged]

LONG-TERM PROFILE VARIABILITY IN ACTIVE GALACTIC NUCLEUS WITH DOUBLE-PEAKED BALMER EMISSION LINES

An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, double-peaked Balmer emission lines,which represent some of the best evidence for the existence of relatively large-scale accretion disks in AGNs. A set of 20 double-peaked emitters have been monitored for nearly a decade in order to observe long-term variations in the profiles of the double-peaked Balmer lines. Variations generally occur on timescales of years, and are attributed to physical changes in the accretion disk. Here we characterize the variability of a subset of seven double-peaked emitters in a model independent way. We find that variability is caused primarily by the presence of one or more discrete "lumps" of excess emission; over a timescale of a year (and sometimes less) these lumps change in amplitude and shape, but the projected velocity of these lumps changes over much longer timescales (several years). We also find that all of the objects exhibit red peaks that are stronger than the blue peak at some epochs and/or blueshifts in the overall profile, contrary to the expectations for a simple, circular accretion disk model, thus emphasizing the need for asymmetries in the accretion disk. Comparisons with two simple models, an elliptical accretion disk and a circular disk with a spiral arm, are unable to reproduce all aspects of the observed variability, although both account for some of the observed behaviors. Three of the seven objects have robust estimates of the black hole masses. For these objects the observed variability timescale is consistent with the expected precession timescale for a spiral arm, but incompatible with that of an elliptical accretion disk. We suggest that with the simple modification of allowing the spiral arm to be fragmented, many of the observed variability patterns could be reproduced.

The magnetic field and circumstellar environment of the helium-strong star HD 36485 =δ Ori C

Extensive Hα spectroscopy of the cool, helium-strong star δ Ori C obtained over two decades has enabled a detailed analysis of the variable Hα emission observed in this sharp-lined and strongly magnetic B3V star. Radial velocity measurements from these and other spectra have also confirmed the binary nature of the star, the first detection of the secondary being provided, and permitted an improved determination of the system’s orbital parameters. The amplitude of the radial velocities and a preliminary spectroscopic analysis indicate that the secondary component is an early A-type star. Disentangling the contribution of the two components to the Balmer line profiles, we determine an effective temperature for δ Ori C slightly larger than previously adopted in the literature. The Hα emission is variable with a period of 1.477 75 ± 0.000 04 d, assumed to be the rotation period of the primary component. After removal of the binary system’s photospheric contribution to the Hα line, we find that the emission arises from two distinct, but asymmetrical, optically translucent circumstellar clouds. When strongest the emission peaks have intensities of approximately 15 per cent of the continuum level at about 150 km s −1 on either side of the line centre, and emission is apparent to ±225 km s −1 ,o r 6R∗ above the photosphere if we assume that the magnetic field forces the circumstellar material into rigid rotation about the star. New 6 cm Very Large Array radio measurements, when combined with archival data, suggest that the radio flux of the star is also variable. An analysis of new and previously published magnetic field observations enabled us to derive a value for the inclination of the rotation axis of i = 12 ◦ ± 3 ◦ and an obliquity of the magnetic axis of β ≤ 52 ◦ . The nature of the emission variability is similar to that of the prototypical helium-strong star σ Ori E, but since the latter object has an inclination of >75 ◦ , δ Ori C provides us with an opportunity to investigate the cool components of the winds and magnetospheres of the helium-strong stars from a different vantage point.