Hγ Lines Research Articles

The Be Phenomenon in Pleione

AbstractThe spectral change of Pleione in the present Be phase (1988-1999) is briefly described. The Hα emission reached its maximum in 1995-1999. The V/R values of Hγ and metallic lines changed from V/R < 1 in 1995 to V/R > 1 in 1998-1999. The broad component of Mg II λ4481 line further weakened in Be phase.The long-term variation in 1968-1999 is shown for several observational quantities. These quantities which reflect various levels from the photosphere up to the outer envelope did not change in a parallel way. The basic unsolved problems are pointed out.

Continuum Flux Excess in Be Stars Determined from Spectral Lines

AbstractWe study the continuum flux excess at λ4471 by comparing the observed He I λ4471 line profiles with non-LTE model line profiles. Assuming that emission of the Hγ line is formed nearly in the same regions of the circumstellar envelope as those where the visible continuum flux excess rises, we estimate the continuum opacity needed to account for the veiling of the He I λ4471 line. The flux excess so derived is then studied as a function of the stellar aspect angle in an attempt to determine the degree of incidence of the envelope geometry near the central star on the continuum flux of Be stars.

The Spectroscopic Age of 47 Tucanae

High signal-to-noise ratio integrated spectra of the metal-rich globular cluster 47 Tuc, spanning the HγHR and Fe 4668 line indices, have been obtained. Jones & Worthey have suggested that the combination of these indices is the best available mechanism for cleanly separating the age-metallicity degeneracy that hampers the dating of distant, unresolved, elliptical galaxies. For the first time, we apply this technique to a nearby spheroidal system, 47 Tuc, for which independent ages, based upon more established methods, exist. Such an independent test of the technique's suitability has not been attempted before but is essential before the technique's application to more distant, unresolved, stellar populations can be considered valid. Because of its weak series of Balmer lines relative to model spectra, our results imply a spectroscopic age of 47 Tuc well in excess of 20 Gyr, which is at odds with the color-magnitude diagram age of 14 ± 1 Gyr. The derived metal abundance, however, is consistent with the known value. Although the observational constraints are restrictive, existing data cannot entirely exclude emission fill-in of the Hγ line as the source of the discrepancy.

Red supergiants in the LMC - III: luminous F and G stars

New BVRI observations for 40 and spectrophotometric measurements for 3 F to G LMC supergiant candidates (and 3 galactic F to G supergiants) are presented. The errors of the BVRI data are 0.01 to 0.03 mag in most cases. The wavelength range of the spectra is 3400 to 6400 Å, their resolution 10 Å. The mean error of the fluxes is 0.03 mag. Spectral indices measuring the strengths of the Hβ, Hγ, Hδ, NaD and CaII H+K lines, the CHα0 and CNβ0 bands, of the Balmer jump and the slope of the continuum redwards are discussed as measures of effective temperature and luminosity on the basis of galactic stars with accurate MK types and parallaxes. The Hγ line and the continuum gradient are very good temperature criteria, the CHα0 band and especially the Balmer jump for luminosity. The luminosity classification given for F to G supergiant candidates in the LMC in the literature is often doubtful. 5 of the 3 stars observed spectrophotometrically turn out to be probably galactic foreground dwarfs on the basis both of the Balmer jump and the comparison of their flux distributions with synthetic ones based on the Kurucz model atmospheres. Surface gravities derived purely on the basis of flux distributions and such ones given by models of stellar evolution agree with each other for dwarfs and giants only. For supergiants the former are about 1.0 dex higher than the latter. As a consequence effective temperatures and metallicities given by these two methods deviate from each other for such stars, too. The intrinsic colours and temperatures of galactic and LMC supergiants do not differ. With absolute magnitudes up to -9.6 mag the upper luminosity limit in the LMC does not exceed that in the Galaxy, where Ia-0 supergiants have MV of up to -9.5 mag. The metallicities of the supergiants show a rather large scatter. Nevertheless the mean metallicities of 0.0 ± 0.09 dex for the Galaxy and -0.6 ± 0.10 dex for the LMC agree well with other observations.

Corotating photospheric clouds in the Be star η Cen

From 819 echelle spectra of η Cen on 13 nights we find strong evidence for corotating gas clouds. Grey-scale images of stacked difference spectra of the combined He I lines at 4144, 4388, 4471, 4922 and 5016 A show diffuse features moving from blue to red with accelerations consistent with the rotation of the star. These are also seen in the Si III 4553 line, but are not very evident in the Hβ and Hγ lines. The same features can be recognized on different nights, from which we infer a rotational period equal to the photometric period of 0.64 d. On many nights emission is present at velocities corresponding to the approaching or receding limb of the star. Although the features are largely stable, clear changes can also be detected. On one night there was a significant increase in emission from a certain region, resulting in the appearance of transient migrating absorption subfeatures sometimes seen in the line profiles of other Be stars. These would normally (incorrectly) be attributed to non-radial pulsation of high degree. These observations are inconsistent with the usually accepted pulsational model for periodic Be stars. We suggest that periodic Be stars can be understood in terms of a model of corotating gas clouds.

Determination of the OB Stellar Population of IZw18 on the Basis of its Hγ and Hδ Absorption lines

On the basis of new spectroscopic observations of the blue compact dwarf galaxy IZw18 in the narrow spectral range between 4000Å and 4500Å absorption components of Hγ and Hδ lines were discovered. Equivalent widths of Hγ and Hδ lines have been measured. From available data the OB population of IZw18 was analyzed.

3.32. The broad component of HeIIλ4686 line in NGC4151

A series of spectral observations of the nucleus of the Seyfert galaxy NGC4151 were obtained with the TV scanner of the 6-meter telescope of SAO, Russia (Nazarova et al. 1997). The nucleus of the NGC4151 was observed repeatedly between 1986 and 1990 in the spectral range from 3900Å to 4950Å. The emission line fluxes were obtained by fitting multiple Gaussians. We parameterise the asymmetry of the HeII λ4686 and Hγ lines by the peak wavelength of the broad Gaussian fitted to the blend at ≈4686Å and at ≈4340Å. Significant changes have taken place in the asymmetry of the Hell line while there is only a gradual and small change in the asymmetry of Hγ line. However, the change in the integrated line flux is exactly opposite. It seems possible that the asymmetric variations of the broad component of Hell line and nearly stable asymmetry in the broad component of Hγ line during the period 1986-1990 might reflect the long-time variations in broad components emitted from HIL and LIL zones respectively. Work is partially supported by RBRF grant 97-02-17625.

UV BRIGHT GALAXIES IN THE CASE LOW-DISPERSION NORTHERN SKY SURVEY

ABSTRACT Spectroscopy and CCD photometry have been obtained to investigate four galaxies reported to have unusually strong UV excess in their objective prism spectra. The spectra of CG 1293 (B152299+302942) and CG 1331 (B155442+295724) suggest they are Seyfert 1 galaxies, with z = 0.1260±0.0002 (standard error) and z = 0.0874±0.0009, respectively. Hα in CG 1293 has a line width (FWHM) of approximately 4 x 103 km s-1. The Hα, Hβ, and Hγ lines in CG 1331 have line widths greater than 7 x 103 km s-1. Spectra for the galaxies CG 1280 (B150126+300206) and CG 1298 (B153025+315554) have no identified emission lines. We find MB=-22.13 for CG 1293 and MB=-22 for CG 1331, for H0=50 km s-1 Mpc-1 and q0=0.5.

Phase‐resolved spectroscopy and photometry of the eclipsing polar EP Draconis (=H1907+690)

AbstractWe present phase‐resolved optical spectroscopy and CCD photometry of the faint eclipsing polar EP Dra (H1907+690). A revised ephemeris is derived which connects all 32000 binary cycles since its discovery by Remillard et al. (1991). We found no difference between spin and and orbital periods of the white dwarf. Changes in the light curve morphology are attributed to a different beaming behaviour which might change on timescales as short as one or several orbital periods. Optical light curve modelling was used to estimate the co‐latitude of the accretion spot, which must be larger than 40°. We have detected Zeeman absorption lines of Hα originating in an accretion halo in a field of 16 MG. The low‐resolution spectra reveal no indication of resolved cyclotron harmonics, which is also suggestive of a relatively low field strength in the accretion region. The Balmer emission lines contain significant contributions from the UV‐illuminated hemisphere of the companion star, whereas the Hell λ4686 emission originates predominantly from the accretion stream. The emission lines have a multi‐component structure and we could single out a narrow emission line in the Hβ and Hγ lines. It radial velocity amplitude suggests a low mass for the white dwarf, if the lines are interpreted as being of reprocessed origin from the whole illuminated hemisphere of the companion star.

Concentration of atomic hydrogen in the ground state in a CH4-H2 microwave plasma

Ground state atomic hydrogen (H:1s 2S1/2) concentrations in the CH4-H2 microwave plasma have been measured using actinometry. These measurements have been made over a wide range of plasma conditions including power inputs of 100–800 W and pressures of 0.5–60 Torr. A trace amount of argon was added to serve as an inert reference gas for concurrent optical emission measurements, in which optical emission intensities from the Hγ line (2p2P0–5d2D) at 434 nm and the Ar* line (4s′[1/2]°−4p′[1/2]) at 750 nm were recorded.

Spectral analysis of H?, H?, and H? lines of a white-light flare (3B/X6.1) on October 27, 1991

We have analyzed time series of Hα, Hβ, and Hγ line profiles taken from a 3B/X6.1 flare which occurred on October 27, 1991 in active region NOAA 6891. Each set of the spectra was taken simultaneously for the first 10 min of the flare event with a low and non-uniform time resolution of 10–40 s. A total of 22 sets of Hα, Hβ, and Hγ were scanned by a PDS with absolute intensity calibration to derive the dynamics and energetics of material in the flare region. Our results are as follows: (1) The Balmer line emitting region is accelerated downward to about 50 km s-1 for the first 50 s and then is decelerated to about 10 km s-1 for the next 150 s. (2) The radial velocity peak precedes the Balmer line intensity peak by about 40 s. (3) The total energy radiated from these Balmer lines is estimated to be 4.9 × 1029 erg.

Time Resolved Optical Spectroscopy of V795 Her

AbstractWe present high resolution optical spectroscopy of the cataclysmic variable (CV) V795 Her. The time- and phase- dependent behaviour of the emission source is examined using two-dimensional image analysis and Doppler reconstruction techniques on the orbital profiles. A clear S-wave modulation of a weak emission feature in the Hβ and Hγ line wings (extending to ~1800 km s−1) is present, with complex asymmetric properties.

Spectral synthesis of spectral populations using Balmer lines

The goal of spectral synthesis is to determine the characteristics of a stellarpop-ulation (age and Initial Mass function) by comparing its observed spectrum to synthetic spectra built by adding contributions of stars (or star clusters) of various ages. When the population is young, its visible spectrum is dominated by Balmer lines. These lines have rarely been used for spectral synthesis because Balmer lines in emission are superimposed to the corresponding stellar absorption lines if there is gas ionized by the hottest young stars, a very frequent case. Still it is here that the absorption Balmer lines are the most useful. An example of a problem that can be attacked only by observing the Balmer lines is that of the possible existence of a low-mass cutoff in the IMF of an extragalactic starburst. This is a very important problem as it may affect our knowledge of star formation in general and also our ideas about evolution of galaxies. The colors of a young starburst as well as most of its spectral features are relatively unaffected by stars of a few solar masses which contribute little to the integrated luminosity and to the ionization and excitation properties. However, as the Balmer lines are much stronger for those stars than for the more massive, hotter ones, one may hope that the strength of the Balmer lines in the integrated spectrum of the starburst can give information on the presence or absence of those hot stars. It has been suggested by Augarde and Lequeux (1985) that the starburst galaxy Mkr 171 = Arp 299 = NGC 3690/IC 694 contains relatively few stars of a few solar masses as the Balmer lines in absorption seem relatively weak. Separation of the absorption from the emission component of those lines requires a good spectral resolution with a high dynamical range. Modern detectors make this possible. We have thus undertaken a program to study the Balmer lines in absorption in extragalactic starburst galaxies. This program has necessitated a new, systematic calibration of the Balmer lines equivalent widths of 70 well-classified galactic stars from spectral types O3 to G0 and luminosity classes I, III, V obtained with the same instrument and in the same conditions as the extragalactic observations (Cananzi et al.,1993,paper I). The study is limited to the Hδ and Hγ lines as they are easily accessible and less contaminated by emission lines than Hα and Hβ. We present here the model we have computed showing the variation of the equivalent widths of a star cluster as a function of the slope x, the higher mass M up , the lower mass M in f of the IMF for 2 histories of star formation: an instantaneous burst in which all stars are formed at the same time on the ZAMS and subsequently evolve in the HR diagram until 107 years and a constant star formation scenario also lasting up to 107 years. The time step used is 106 years. Because of the non-unicity of the solution inherent to spectral synthesis model, constraints like L Bol , L V, LB, LU, the number of Lyman continuum α photons and the Hβ luminosity (Osterbrock, 1989) have been synthesized as well to compare with what we observe in galaxies (Cananzi et al.,1993: paper II)

The HeI λ4471 line behaviour of 31 Peg

In this paper we report the spectroscopic behaviour of 31 Peg in the HeI λ4471, MgII λ4481 and the Hγ lines at four observing dates. The behaviour of the HeI line indicates that perhaps there exists a photospheric activity and/or some exophotospheric perturbing effect acting on the stellar photosphere.

Study of the HeI λ4471 line-profile of Be stars

In this paper we study the veiling effect and the strength of an extra emission-like component filling partially the HeI λ4471 line of Be stars. It is shown that this component is roughly correlated with the emission in the continuum and in the Hγ line.

Mass loss, magnetic field and chemical inhomogeneities in the He-weak star HD 21699

HD 21699 is a He-weak star whose longitudinal magnetic field ranges from − 1.3 to +1.1 kG (Brown et al. 1985). Its effective temperature, Teff = 15900 K, and its gravity, log g = 4.0, were determined by Wolff (1990) from photometry of the Balmer discontinuity and from measurements of the Hγ line. HD 21699 was reported to exhibit remarkable variations in the C IV ultraviolet resonance lines at 1548 and 1551 Å (Shore et al. 1987). These variations occur with the same period, 2d49 (Percy 1985), as the magnetic variations and the photometric variations in the optical region. Similar UV line variations could be found only in two other He-weak stars, HD 5737 and HD 79158. They were interpreted as an evidence of the occurrence of outflowing winds controlled by the magnetic field. Furthermore, Shore et al. emphasized that no lines in IUE spectra other than C IV, and possibly Si IV, show any statistically significant variation. Recently, irregular brightening of a few hundredths of magnitude, superimposed over the periodic variations, were observed in the U photometric band (Vetö 1993); their origin is currently unknown.

Variation of Broad Optical Emission Lines in AGN's

AGN optical spectra (4000–5000Å) have been obtained with the TV scanner of the 6-m telescope at Special Astrophysical Observatory (N. Arkhiz-North Caucasus) from 1986 to now. Most spectra were obtained with dispersion of 1 Å/channel and with 3–4Å spectral resolution and signal-to-noise ratio S/N=10–25 for individual spectra. NGC 4151, NGC 3516, NGC 5548 and NGC 7469 are the main sources of the programme and are also being used in international AGN watch programmes for diagnosis, estimation of the size and structure of the BLR.NGC4151:In 1987 the broad components of the Hβ and Hγ lines decreased strongly (on about 65% as compared with 1986) and fell to a level comparable to that of 1984. In 1988 they increased up approximately to the level of 1986. During the photometrically low state of NGC 4151 satellites of the strong Hβ, Hγ, Hδ and He II4686Å lines were suspected at radial velocities of +9400 km/s and −7500 km/s. The data are could be interprite a two-jet model with jet velocity of 8400–24000 km/s. (Bochkarev et al., 1989). Analysis of the spectra shows that the broad component of HeII λ 4686Å changed its asymmetry over 6 years. Bochkarev et al. (1992), Nazarova et al. (1993) discussed a possible explanation of profile HeII λ 4686Å behavior by involving a precession of cones of ionizing radiation.NGC5548:Cross-correction of the optical emission line light curves with the UV continuum light curve reveals that the lines respond to continuum variations with a time delay from 7 days for HeII 4686Å to 18 days for Hβ. Hγ responds more rapidly than the lower order Balmer lines and there is a general trend towards higher amplitude variations in higher-order lines. The time lags for the line variations are consistent with the general pattern of radial ionization stratification of the BLR. During 1988–89 Fe II in blend 4130Å varies with an amplitude of aproximately 20% about the mean, similar the amplitude of the Hβ variations and Balmer continuum.NGC3516:Variations of Hβ during 1986–88 were small (20%), the shape of the profile (including the assymetry) did not change, but Hγ - to Hβ ratios of the profile integrated intensities of broad component increased from 0.43 in 1986 to 0.8 in 1988. The 30% variations of continuum on characteristic time scale 10–15 days during the spring of 1988 were not accompanied by any noticeable changes in the line profile (Bochkarev et al., 1990).

PROFILES OF H BALMER LINES EMITTING FROM A LASER-INDUCED SILANE PLASMA

Profiles of Hα,Hβ and Hγ lines, cmited from a TEA CO2 laser induced silane plasma, are measured with an optical multichannel analizer (OMA Ⅲ) The experimental results show that FWHM (full width of half maximum) of the three lines increases with the main quantum number of the corresponding upper level of the transiti ons, i.e. △λ1/2(Hα)1/2(Hβ)1/2(Hγ), this suggests that the dominant broadening mechanism of the lines is Stark broadening. Fitting the measured Hα profile to theretical data of Stark broadening, two parameters of the plasma are obtained: average electron density N = 1017cm-3 and electron temperature T = 40 000 K. From time tesolved measurements of Hβ profile, a curve of electron density versus time is derived.

Low-dispersion spectroscopy of blue stars from the UK Schmidt Telescope UBVRI survey

We present analyses of SAAO low-dispersion spectra and COSMOS photographic photometry of 49 B-type stellar candidates selected from the United Kingdom Schmidt Telescope (UKST) UBVRI survey. Four of the stars are possibly normal B-type stars at large z-distances from the galactic plane. For these objects, we present approximate atmospheric parameters based on a comparison of the stellar Hγ lines with theoretical profiles, and spectral types based on MK classification and the Johnson Q parameter. Spectral types are also provided for the remaining stars, which are OB-type subdwarfs.

A comparison of balmer α, β, γ emission in collisions between H1+, H2+, H3+ and He, Ne, Ar

Balmer α, β, γ emissions have been measured in collisions between H1+, H2+, H3+, and He, Ne, Ar in energy range of 50-150keV, using TN-1710 optical multichannel analysis system (OMA). The emission cross sections of Hα, Hβ, Hγ lines are given. The experimental results demonstrate that the emission cross sections of Hα,β,γ lines in H3+ +He, Ne, Ar collision systems are larger than those in H1+, H2+ +He, Ne, Ar, respectively.