Hβ Flux Research Articles

The supernova remnant G 6.4-0.1 and its environment

Flux calibrated CCD images, in the Hα + (N ), (S ), and (O ) emission lines, of a wide field around the supernova remnant G 6.4-0.1 are presented. The low ionization images identify a front of enhanced (S )/Hα + (N ) ratio along the east- west direction. This front is very well correlated with the filamentary radio emission of the remnant as well as with molecular CO emission and may indicate the interaction of the primary blast wave with molecular clouds present in the vicinity of the remnant. We estimate a total Hα flux, corrected for interstellar extinction, of 2 × 10 −8 erg s −1 cm −2 , and a total (S ) flux of 1.1 × 10 −8 erg s −1 cm −2 .T he Hα + (N  )a nd (S) images provide evidence for the presence of emission from shock heated gas to the south-west and to the east of the bulk of the known optical emission, implying that the primary shock wave is able to drive radiative shocks into the interstellar clouds. The image in the medium ionization line of (O )5007 A does not reveal any filamentary structures. On the contrary, the emission is diffuse and very weak, close to our detection limit of 5 × 10 −17 erg s −1 cm −2 arcsec −2 (3σ), and appears to be mainly present in the south-east to north-west areas of the remnant. The long-slit spectra indicate significant extinction in all positions observed, while the measured variations are within the 3σ error. The (O ) emission in the spectra, whenever present, is weaker than the Hβ flux suggesting shock velocities around 70 km s −1 or less all around the remnant in accordance with the (O ) imagery. Thus, the low shock velocities are a common characteristic of G 6.4-0.1 and not just of the areas where the spectra were acquired. The average sulfur line ratio suggests postshock electron densities below 120 cm −3 at the 3σ limit.

Optical Imaging and Spectroscopy of the HiiRegion G353.2+0.9 in NGC 6357 and Its Relation to Pismis 24

G353.2+0.9 is the brightest H II region in NGC 6357. The present observations imply that it is optically thin and contains ~300 M⊙ of ionized gas. It is probably expanding into the surrounding medium as a result of its higher thermal pressure. Its chemical composition is similar to that found in other H II regions located at comparable galactocentric distances. The inner regions are probably made of thin shells and filaments, whereas extended slabs of material, probably shells seen edge-on, are found in the periphery. Extinction, although abnormal, is quite uniform but somewhat larger in the brightest optical regions. The radio continuum and Hα emission maps are very similar, indicating that most of the optical nebula is not embedded in the denser regions traced by molecular gas and by the presence of IR sources. About 1050 UV photons per second are required to produce the Hβ flux from the 113 × 10' region surrounding Pis 24. Thus, most of the energy powering G353.2+0.9 and the surrounding environment is produced by the O3–O7 stars in Pis 24. Practically all Two Micron All Sky Survey sources with large near-infrared excesses are within G353.2+0.9, indicating that the most recent star-forming process occurred in this region. Some amount of heating and ionization is due to these stars. The formation of the Pis 24 cluster preceded and caused the formation of this new generation of stars and may be responsible for the present-day morphology of the entire NGC 6357 region.

An Active Galactic Nucleus Sample with High X‐Ray–to–Optical Flux Ratio from RASS. II. Optical Emission Line Properties of Seyfert 1–Type Active Galactic Nuclei

This work studies the optical emission line properties of a sample of 155 low-redshift bright X-ray-selected ROSAT Seyfert 1-type active galactic nuclei for which adequate signal-to-noise ratio spectroscopic observations are available. We measured emission-line properties by performing multicomponent fits to the emission-line profiles, covering the effect of blended iron emission. We also obtained continuum parameters, including 250 eV X-ray luminosities derived from the ROSAT database. In addition, the measured properties are gathered for a correlation analysis, which confirms the well-known relations between the strengths of Fe II, [O III] emission and the X-ray slope. We also detect striking correlations between Hβ redshift (or blueshift) and flux ratios of Fe II to Hβ broad component and [O III] to Hβ narrow component. These trends are most likely driven by the Eddington ratio.

Extreme Emission Line Outflows in the GPS Source 4C 12.50 (PKS 1345+12)

AbstractWe present high resolution spectra (0.7 Å/pix) of the GPS source 4C 12.50 with large spectral coverage (˜4500 Å) taken with the 4.2 m William Herschel Telescope, La Palma. The slit was aligned along PA 160° to include the nucleus and emission line region to the NW. An asymmetric halo extending 20 kpc NW and 12 kpc SE from the nucleus is clearly seen. At the position of the nucleus we observe unusually broad forbidden emission line components (broadest component: FWHM ˜ 2000 km s−1), blue shifted by up to 2000 km s−1 with respect to the halo of the galaxy and HI absorption. We interpret this as material in outflow. We measure E(B–V) = 1.44 for the broadest, most kinematically disturbed component, corresponding to an actual Hβ flux 130 times brighter than that measured. We calculate an upper limit for the mass of the line emitting gas of order 106 M⊙ for both the intermediate and broad components. Our results are consistent with 4C 12.50 being a young radio source.

H [CSC]ii[/CSC] Emission from a Complete Spectroscopic Survey of B[CLC]e[/CLC] Stars in [CLC]h[/CLC] and χ Persei

We describe data for emission-line B stars observed in a spectroscopic survey of h and χ Persei. The survey is complete to V = 12.5 and covers an area of ~1100 arcmin2 roughly centered on the two clusters. We detect 32 Be stars; some have low Hα emission strength. Seven of these are new identifications; seven others are confirmations of Be stars previously identified using photometry. Five of the observed Be stars show significant Hα profile variations from epoch to epoch. We show that spectral indices yield physical characteristics of the H II emission region. This automatic method is robust and easily applied to large spectroscopic samples. We infer Hα : Hβ flux ratios of 2–5 and observe a linear relationship between Hα emission and J-K color for these stars. We include a Hertzsprung-Russell diagram for the B-type stars in the clusters.

Hydrodynamic Simulations of Flares on Accretion Disks

We have constructed a hydrodynamic simulation of flares on the accretion disks of cataclysmic variable stars. In these flares the disk photosphere is heated by a beam of suprathermal electrons. The beam energy flux, beam duration, position in the accretion disk, and accretion disk temperature were varied in 20 flare simulations. All the flare simulations show that above a site of maximum heating the gas is blown upward from the disk. Below this point the gas is compressed and heated. A non-LTE radiative transfer program calculates the resulting continuous emission and Balmer line radiation from the flare. The temporal development of each flare model is followed by calculating the radiation at 15–20 time steps. The Hβ line flux from accretion disks is estimated for 20 dwarf novae and 12 nova and nova-like systems by using information gathered from the literature. We then use a simple approximation for the rate of flaring across an accretion disk to see whether flares can account for all the Hβ emission. The rate of flickering observed in cataclysmic variables is used as a constraint on this model. Using flickering rates from one study we find that if each observed flicker is one magnetic flare, then flares can account for only 1%–2% of the Hβ emission. A much higher flare rate can account for the observed Hβ emission if flickering studies underestimate the true rate of flaring. A flare avalanche model may account for both the observed Hβ flux and the observed flickering.

A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies

We have compiled a list of 83 objects classified as Narrow-Line Seyfert 1 galaxies (NLS1s) or known to have a broad Balmer component narrower than 2 000 km s-1 . Of these, 19 turned out to have been spectroscopically misidentified in previous studies; only 64 of the selected objects are genuine NLS1s. We have spectroscopically observed 59 of them and tried to characterize their Narrow and Broad-Line Regions (NLR and BLR) by fitting the emission-lines with Gaussian and/or Lorentzian profiles. In most cases, the broad Balmer components are well fitted by a single Lorentzian profile, confirming previous claims that Lorentzian rather than Gaussian profiles are better suited to reproduce the shape of the NLS1s broad emission lines. This has consequences concerning their FWHM s and line ratios: when the broad Balmer components are fitted with a Lorentzian, most narrow line regions have line ratios typical of Seyfert 2s while, when a Gaussian profile is used for fitting the broad Balmer components, the line ratios are widely scattered in the usual diagnostic diagrams (Veilleux & Osterbrock [CITE]); moreover, the FWHM of the best fitting Lorentzian is systematically smaller than the FWHM of the Gaussian. We find that, in general, the [O III] lines have a relatively narrow Gaussian profile (~200-500 km s-1 FWHM ) with often, in addition, a second broad (~500-1 800 km s-1 FWHM ), blueshifted Gaussian component. We do not confirm that the [O III] lines are weak in NLS1s. As previously suggested, there is a continuous transition of all properties between NLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limit of 2000 km s-1 used to separate the two species is arbitrary; R 4570 , the ratio of the Fe II to the Hβ fluxes, could be a physically more meaningful parameter to distinguish them.

Oii] As a Tracer of Current Star Formation

[O II] λ3727 is often used as a tracer of star formation at intermediate redshifts (z ≳ 0.4), where Hα is not easily observed. We use the spectrophotometric data of the Nearby Field Galaxy Survey to investigate the range and systematic variation in the observed [O II]/Hα emission-line ratio as a function of galaxy luminosity at low redshift. We find that the observed [O II]/Hα ratio varies by a factor of 7 at luminosities near MB*. The [O II]/Hα ratio is inversely correlated with luminosity. The scatter in the [O II]/Hα ratio and the dependence of the ratio on luminosity are due in equal parts to reddening and to the metallicity-dependent excitation of the interstellar medium. The uncertainty in star formation rates derived from [O II] fluxes is therefore large. If Hα cannot be observed, high signal-to-noise ratio Hβ fluxes are much preferable to [O II] fluxes for deriving star formation rates. We present several purely empirical corrections for extinction.

A Link between the Hβ Equivalent Width, Profile Width, BLR Size, and Optical Luminosity from a Small Sample of Well-studied Active Galactic Nuclei

We present diagrams of the relationship between the broad Hβ emission-line parameters and the continuum luminosity obtained from a sample of 31 well-studied Seyfert 1.0–1.5 galaxies and quasars. The equivalent width of the Hβ line is inversely correlated with the continuum luminosity at 5100 A as EW ~ L, which seems to be comparable to that obtained by other authors for the Lyα. So, we have detected, although very marginally, a Baldwin effect in the Hβ line. The remarkably small scattering of the Hβ equivalent widths probably indicates approximately the same spectral energy distribution from optics to ionizing radiation, nearly the same covering factor, and nearly isotropic continuum emission, although some of these agents can show small systematic changes with luminosity. The intrinsic Baldwin effect for the Hβ is clearly seen only in NGC 5548. Considering the observed lag-luminosity and lag–line-width dependences we suppose that it might be caused by full ionization of clouds. We compute the linear regression parameters (the slopes and intercepts) of the relationship between the Hβ and optical continuum fluxes. In some cases, the regression parameters derived from the homogeneous data sets are significantly different for different observational periods. The lag of the Hβ response to continuum variations shows a strong correlation with the luminosity. Combining the regression results on time delay and rms widths of the Hβ line, we obtained the following mass-luminosity relationship for AGNs: L ∝ M1.9±1.1.

The influence of close binary evolution on the age determination of starburst regions

Using a population number synthesis code and detailed massive star evolutionary calculations, we investigate the effect of close binary evolution on Hα and Hβ emission-line strength variation in starburst regions. The Hβ line strength especially, is considered as a good age indicator. We demonstrate that the formation of rejuvenated accretion stars (Blue Stragglers) through RLOF lengthens the life-time of the Hβ flux and makes the age determination of a starburst regions ambiguous. We separately calculate the effect of Wolf-Rayet stars and of X-ray binaries on Hα and Hβ and conclude that both are of minor importance.

Ultraviolet Imaging of the Irregular Galaxy NGC 4449 with the Ultraviolet Imaging Telescope: Photometry and Recent Star Formation History

The bright Magellanic irregular galaxy NGC 4449 was observed during the Astro-2 Space Shuttle mission by the Ultraviolet Imaging Telescope (UIT), which obtained images of a 40' field centered on the galaxy in two broad far-ultraviolet (FUV) bands centered at 1520 and 1620 A, with 3''-5'' spatial resolution. Together with Hα and Hβ fluxes from ground-based Fabry-Perot images, these data are analyzed in order to explore the recent star formation history of NGC 4449. Maps of the Hα-to-FUV and FUV-to-blue continuum flux ratios are presented and interpreted using evolutionary synthesis models. Photometry is presented both for 22 apertures containing large OB complexes and for 57 small apertures containing compact FUV-emitting knots. The OB complexes along the northern edge of the visible system have high Hα-to-FUV ratios and thus appear to be more dominated by the current generation of stars than are other parts of the galaxy. However, young sources do exist elsewhere and are particularly conspicuous along the bar. The small-aperture analysis shows three candidate regions for sequential star formation. Surface brightness profiles are consistent with an exponential disk in both the FUV and the optical continuum.

Planetary Nebulae in the NRAO VLA Sky Survey

The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog were used to detect radio emission from the 885 planetary nebulae north of J2000 declination δ = -40° in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae. We identified 680 radio sources brighter than about S = 2.5 mJy beam-1 (equivalent to T ≈ 0.8 K in the 45'' FWHM NVSS beam) with planetary nebulae by coincidence with accurate optical positions measured from Digitized Sky Survey (DSS) images. Total extinction coefficients c at λ = 4861 A were calculated for the 429 planetary nebulae with available Hβ fluxes and low free-free optical depths at 1.4 GHz. The variation of c with Galactic latitude and longitude is consistent with the extinction being primarily interstellar and not intrinsic.

Sakurai's object: the ionized nebula at radio wavelengths

Sakurai's object (V4334 Sgr) is a planetary nebula nucleus which is undergoing its final helium shell flash. This is the first of these rare and important events to be observable with non-optical instruments. We report the first radio detection, using a short (2-h) observation with the Very Large Array (VLA) at 4.86 GHz. The radio emission structure is coincident with the 34-arcsec diameter planetary nebula seen in optical emission lines. We find a statistical distance ∼ 3.8 ± 0.6 kpc, with a range of 1.9 < D < 5.3 kpc, depending on the planetary nebula (PN) mass. While we have no direct evidence for a new (post-flash) stellar wind, we estimate an upper limit to the mass-loss rate due to any such wind of 1.7 × 10−7 M⊙ yr−1. The number of emitting knots in the radio-visible nebula indicates an electron density of ∼ 2 × 108 m−3 in those knots, and a total emitting ionized mass of ∼ 0.15 M⊙, at an assumed distance of 3.8 kpc. The radio flux density indicates an Hβ flux of ∼ 6 × 10−16 W m−2, suggesting an extinction E(B − V) ∼ 1.15, comparable with reddening estimates in the direction of V4334 Sgr.

Measurement of an Active Galactic Nucleus Central Mass on Centiparsec Scales: Results of Long‐Term Optical Monitoring of Arp 102B

The optical spectrum of the broad-line radio galaxy Arp 102B has been monitored for more than 13 yr to investigate the nature of the source of its broad, double-peaked hydrogen Balmer emission lines. The shape of the lines varied subtly; there was an interval during which the variation in the ratio of the fluxes of the two peaks appeared to be sinusoidal, with a period of 2.16 yr and an amplitude of about 16% of the average value. The variable part of the broad Hα line is well fitted by a model in which a region of excess emission (a quiescent hot spot) within an accretion disk (fitted to the nonvarying portion of the double-peaked line) completes at least two circular orbits and eventually fades. Fits to spectra from epochs when the hot spot is not present allow determination of the disk inclination, while fits for epochs when it is present provide a measurement of the radius of the hot spot's orbit. From these data and the period of variation, we find that the mass within the hot spot's orbit is 2.2 -->+ 0.2−0.7×10 -->8 M☉, within the range of previous estimates of masses of active galactic nuclei. Because this mass is determined at a relatively small distance from the central body, it is extremely difficult to explain without assuming that a supermassive black hole lies within Arp 102B. Our collection of spectra allows us to apply several tests to models of the source of the double peaks. The ratio of Hα to Hβ flux at a given velocity displays no turning points or points of inflection at the velocity associated with the blue peak in flux; thus, this peak should not correspond to a turning point in physical conditions. This behavior is consistent with simple accretion disk and, possibly, spiral shock models but not with models that attribute the double peaks to separate broad-line regions around a binary black hole or to broad, subrelativistic jets. The lack of systematic change in the velocity of the blue peak over time provides a further constraint on binary broad-line region models; this yields a lower limit on the mass of such a binary black hole system of at least 1010 M☉. The variability properties of the double-peaked emission lines in Arp 102B therefore continue to favor an accretion disk origin over other models.

Sakurai's Object—A Possible Final Helium Flash in a Planetary Nebula Nucleus

UBVRIJK photometry and optical spectroscopy of Sakurai's object and direct imaging of the surrounding nebulosity are presented. The progenitor star is identified as a faint blue object of mj = 21. The circular planetary nebula has a diameter of 32'', its distance, derived from the Hβ flux, is 5.5 kpc. At present, the object is a luminous supergiant of approximate spectral type F2, having MV = -4.1, and has clear indications of hydrogen underabundance, with carbon and oxygen overabundance. Its photospheric radial velocity is the same as that of the surrounding planetary nebula, indicating that they are associated, and that there is currently no mass loss by a thick wind. A marginal IR excess suggests the presence of some hot dust.

Chemical Abundances from Planetary Nebulae in Elliptical Galaxies

Currently over 2000 Planetary Nebulae (PN) have been detected in Local Group E and S0 galaxies by on/off band [O III]5007Å CCD photometry. PN can currently be detected out to Fornax and Virgo clusters.The magnitude of the brightest PN in the nearest elliptical galaxy (NGC 205) is m5007 20.7 (Ciardullo et al, 1989); for NGC 5128 (Cen-A) it is 23.5 (Hui et al, 1993a) and ≥ 25.6 for Virgo ellipticals (Jacoby et al, 1990). Given the relation between m5007 and line flux:m5007 = −2.5 log F5007 − 13.74the typical Hβ fluxes are ≤1.5×10-16 ergs cm−2 s−1 for NGC 5128 PN and ≤ 2.5×10−17 for Virgo PN. Obtaining spectra of these faint emisison lines is clearly a challenge. The only PN spectra studied in Local Group galaxies are 1 PN in M32 (NGC 221) (Log F(H/β) = −14.9; Jenner et al, 1979) and recently 15 in NGC 205 (Jacoby et al, 1995). None of the spectra are of high quality and the Te diagnostic line [O III]4363Å was not detected. There is evidence of possible high N abundance in the M32 PN.

A Clustering Method Applied to the Analysis of Planetary Nebulae

Intensities of the observed spectral lines, radio fluxes and Hβ fluxes are used for the classification of planetary nebulae by centroid method of taxonomical analysis. Two variants of classification are proposed. The first one– in the three–dimensional space of relation of intensity of spectral lines He II λ 4686/HeI λ 4471, [OIII] λ 4959+5007/[OII] λ 3726+29, [OIII] λ 4959+5007/[OIII] 4363. The second variants is the classification in the three-dimensional space with cooordinates being radio flux, Hβ flux and [OIII] λ 4959+5007 intensity. The membership of classes (taxons) are presented. In the diagram joining the planetary nebula descriptors pairwise there are regions of complete (or predominant) of nebulae belonging to the same taxon, but there are also some regions of overlap. The corresponding taxons are not isolated but merge continuously into one another.

Luminosities of Central Stars of PN in the Galactic Bulge

A calibration of the nebular intensity of [O III] 5007 (relative to Hβ) in terms of stellar bolometric corrections is presented. This calibration (restricted to low- and medium-excitation PN) is based exclusively on the results of non-LTE model atmosphere analyses of absorption-line profiles in the spectra of bright central stars of PN (Méndez et al. 1988, A&amp;A 190, 113 and subsequent papers). Knowing the bolometric corrections, the distance to the Galactic center, the amount of interstellar extinction and the visual apparent magnitudes (Tylenda et al. 1989, A&amp;AS 77, 39) of central stars of PN in the direction of the Galactic center, luminosities for 20 of these central stars are obtained without any assumptions about nebular properties. The luminosities obtained with this method are substantially higher than those obtained for the same objects by Pottasch and Acker (1989, A&amp;A 221, 123) and Tylenda et al. (1991, A&amp;A 246, 221). The most probable explanation for this discrepancy is that luminosity estimates based on assumptions about nebular properties are too low, because many PN are not completely optically thick in the H Lyman continuum and/or because many ionizing photons in these PN are being absorbed by nebular dust. Which of the two effects is more important cannot be decided without solving the problem of the discrepancy between extinction determinations based on the Balmer decrement versus extinction determinations based on radio and Hβ fluxes (the radio-Hβ extinctions are too low).

Planetary Nebulae by the Strong [NII] Emission Lines

The sample of planetaries with the strong [NII] emission lines are analysed. All available parameters are discussed. The enrichments of all elements and the tendency to rather low surface brightness of ne bulae in Hβ flux are remarked. The deficiency of hydrogen in envelopes is proposed as the possible reason of observational spectra.

Further Models of Planetary Nebula Spectral Evolution

Four new calculations of planetary nebulae spectral evolution are presented, as in Volk (1992). These models use the 0.64 M⊙ central star evolution track of Schönberner (1983) but with the rate of evolution accelerated by a factor of 2, as the original models evolve to the planetary nebula phase too slowly to match the observations. Models were calculated for mass-loss rates of 2.1 × 10−5 and 5.2 × 10−5 MM⊙ yr−1 using solar composition and silicate dust, and using the average observed planetary nebula composition and graphite dust. An interacting winds shell was assumed to form. The model results were combined with an assumed Galactic distribution of 25000 planetary nebula to simulate a variety of observables including V magnitudes, Hβ fluxes, the IRAS colours, the 5 GHz radio flux densities, and the nebular radii.