Continuum Energy Distribution Research Articles

A Two-Temperature Model for LBVs

The continuum energy distributions of R127 and R110 in the outburst phase are fitted by use of a optically envelope model. Both stars show two peaks in the continuum energy distributions in which one lies in the short-wavelength range (near 1250Å) and the other in the optical band. We suggest that the fluxes in the UV and optical bands may have different origins: the UV flux comes from the central star and the optical flux comes from the expanded optically envelope. We construct such a model for LBVs with the use of two LTE atmosphere models with different temperatures, and find it to be in satisfactory agreement with the observed spectral energy distributions of R127 and R110.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Free‐Free Spectral Energy Distributions of Hierarchically Clumped HiiRegions

In an effort to understand unusual power-law spectral slopes observed in some hypercompact HII regions, we consider the radio continuum energy distribution from an ensemble of spherical clumps. An analytic expression for the free-free emission from a single spherical clump is derived. The radio continuum slope (with F_\nu \nu^\alpha) is governed by the population of clump optical depths N(tau), such that (a) at frequencies where all clumps are thick, a continuum slope of +2 is found, (b) at frequencies where all clumps are optically thin, a flattened slope of -0.11 is found, and (c) at intermediate frequencies, a power-law segment of significant bandwidth with slopes between these two limiting values can result. For the ensemble distribution, we adopt a power-law distribution N(tau) tau^{-\gamma}, and find that significant power-law segments in the SED with slopes from +2 to -0.11 result only for a relatively restricted range of $\gamma$ values of 1 to 2. Further, a greater range of clump optical depths for this distribution leads to a wider bandwidth over which the intermediate power-law segment exists. The model is applied to the source W49N-B2 with an observed slope of \alphab +0.9, but that may be turning over to become optically thin around 2 mm. An adequate fit is found in which most clumps are optically thin and there is little shadowing of rearward clumps by foreground clumps (i.e., the geometrical covering factor C<<1). The primary insight gained from our study is that in the Rayleigh-Jeans limit for the Planck function that applies for the radio band, it is the distribution in optical depth of the clump population that is solely responsible for setting the continuum shape, with variations in the size and temperature of clumps serving to modulate the level of free-free emission.

The LBV nature of Romano's star (GR 290) in M 33

We report the first spectroscopic study of the LBV candidate GR 290 in M 33 (Romano's star) taken in February 2003, showing, besides prominent hydrogen and He  emission lines, the 4630-60 A blend and weak He  4686 A emission typical of Of stars. Our broad-band photometry shows that the star was observed during a phase of minimum optical luminosity, with B = 17.91 ± 0.03, and a slightly positive colour index, which we tentatively attribute to an anomalous continuum energy distribution. We argue that GR 290 is indeed an LBV star presently in a high temperature phase, that should be followed - also in a short time - by ample spectroscopic and associated photometric variations.

Peculiarities of the UV continuum energy distribution for T Tauri stars

In the UV spectra of BP Tau, GW Ori, T Tau, and RY Tau obtained with the Hubble Space Telescope, we detected an inflection near 2000 A in the F λ c (λ) curve that describes the continuum energy distribution. The inflection probably stems from the fact that the UV continuum in these stars consists of two components: the emission from an optically thick gas with T 2000 A originates not in the accretion shock but in the inner accretion disk. Previously, a similar conclusion was reached for six more classical T Tau stars. Therefore, we believe that the high-temperature continuum can be associated with the radiation from the disk chromosphere. However, it may well be that the stellar chromosphere is its source.

The Infrared Spectral Energy Distribution of the Seyfert 2 Prototype NGC 5252

The complete mid- to far-infrared continuum energy distribution collected with the Infrared Space Observatory of the Seyfert 2 prototype NGC 5252 is presented. ISOCAM images taken in the 3-15 μm show a resolved central source that is consistent at all bands with a region of about 1.3 kpc in size. Because of the lack of ongoing star formation in the disk of the galaxy, this resolved emission is associated with either dust heated in the nuclear active region or bremsstrahlung emission from the nuclear and extended ionized gas. The size of the mid-IR emission contrasts with the standard unification scenario envisaging a compact dusty structure surrounding and hiding the active nucleus and the broad-line region. The mid-IR data are complemented by ISOPHOT aperture photometry in the 25-200 μm range. The overall IR spectral energy distribution is dominated by a well-defined component peaking at ~100 μm, a characteristic temperature of T 20 K, and an associated dust mass of 2.5 × 107 M☉, which greatly dominates the total dust mass content of the galaxy. The heating mechanism of this dust is probably the interstellar radiation field. After the contribution of this cold dust component is subtracted, the bulk of the residual emission is attributed to dust heated within the nuclear environment. Its luminosity consistently accounts for the reprocessing of the X-ray to UV emission derived for the nucleus of this galaxy. The comparison of NGC 5252's spectral energy distribution with current torus models favors large nuclear disk structure on the kiloparsec scale.

The recovery of the old nova RS Car (1895)

Low-resolution spectra, taken at La Silla (ESO), identify the old nova RS Car (1895) as a ∼18 mag star located 7 arcsec southwest from the previous published position. This suggests a much brighter absolute magnitude of the old nova, Mv∼5.4, than previously suspected. The spectrum reveals a continuum energy distribution typical of optically thick accretion discs and quite a high excitation state of the gas. The possible detection of the AlO λ4843 emission band is discussed.

Analysis of the HST ultraviolet spectra for T Tauri stars: RY Tau and HD 115043

The ultraviolet spectra of the stars RY Tau and HD 115043 from the Hubble Space Telescope are analyzed. RY Tau belongs to the classical T Tauri stars, while HD 115043 is a young (t~3×108 years), chromospherically active star. The most intense emission lines were identified, and their fluxes were measured. Low-resolution spectra of RY Tau and HD 115043 in the wavelength range 1160–1760 A exhibit almost the same set of emission lines. However, first, the luminosity of RY Tau in these lines is approximately a factor of 300 higher than that of HD 115043, and, second, the relative line intensities differ greatly. The intensity ratio of the C IV λ1550, Si IV λ1400, and NV λ1240 doublet components is close to 1: 2 in the spectra of both stars. Judging by the continuum energy distribution, the spectral type of RY Tau is later than that of HD 115043. Synchronous flux variability in the C IV λ1550 and He II λ1640 lines in a time of ~20 min was detected in RY Tau. The flux rise in these lines was accompanied by a redshift of the intensity peak in the profiles by~50 km s−1. Intermediate-resolution spectra are used to study line profiles in the spectrum of RY Tau. In particular, the profiles of (optically thin) Si III]λ1892 and C III]λ1909 lines were found to be asymmetric and about 300 km s−1 in width. The (optically thick) C IV λ1550 doublet lines have similar profiles. The Mg II λ2800 doublet lines are also asymmetric, but their shape is different: they consist of a broad (≃750 km s−1 at the base) emission component on which an interstellar absorption line shifted from the line symmetry center by about 20 km s−1 is superimposed. The intensity ratio of the Mg II λ2800 doublet components is≃1.4. Whether there are molecular hydrogen lines in the spectrum of RY Tau is still an open question. It is shown that the emission lines in the ultraviolet spectrum of RY Tau cannot originate in a hydrostatically equilibrium chromosphere. It is argued that quasi-steady accretion of circumstellar matter is responsible for the emission.

Applications of Narrow-Band Photometry in the Study of Peculiar Red Giants

Narrow-band photometry, carried out with filters or spectrum scanners, is useful for measuring molecular bandstrengths and continuum energy distributions in late-type stars. This review emphasizes observations by the writer on three different multicolor photometric systems in the near infrared (0.75 − 4.0 μm); a summary of available data is given. While applications to date have been primarily qualitative (classification, recognition of peculiarities, relative temperatures), future applications are expected to be quantitative (determinations of effective temperatures, luminosities, and abundances) and based upon comparison with synthetic spectra.

RXTE,ROSAT,EUVE,IUE, and Optical Observations through the 45 Day Supercycle of V1159 Orionis

A complete 45 day supercycle of the cataclysmic variable V1159 Ori comprising a superoutburst and eight normal outbursts was observed. Coverage included ground-based optical observations as well as observations with RXTE for 38 days, ROSAT for 34 days, IUE for 27 days, and Extreme Ultraviolet Explorer (EUVE) for 10 days. The resulting light curves reveal that the optical and UV light variations are inversely correlated with the RXTE and ROSAT fluxes, with the largest change in intensity occurring in the ROSAT bandpass. There is no evidence for a strong EUV/soft X-ray component during outburst. An outflowing wind is evident from the C IV line profile during each brief outburst as well as the superoutburst. The transitions from outburst states of the disk to quiescent states take place on timescales of hours. Accretion disk models can fit the UV line and continuum energy distributions near outburst only if the disk radial temperature profile is modified from the standard case to produce a hotter distribution in the outer annuli. The high mass transfer rate, the hot disk distribution, and the similarity of outbursts and superoutbursts argue for outside-in outbursts in this system.

The continuum energy distribution of single galactic Wolf-Rayet stars

For eleven single galactic WR stars, the continuum energy distribution from the UV to the radio was obtained from literature data. Although a power law with α = 2.79 could describe all the distributions, there appear to be deviations that depend on stellar type.

Physics of Radiatively Driven Winds by High Angular Resolution Observations (HARO)

AbstractNumerous models have been developed during the last two decades which try to fit a small number of “classical” observables as closely as possible (i.e Hα line profile and continuum energy distribution or polarization data). Nevertheless, little has been done to include High Angular Resolution Observations (HARO) in simulations in spite of the fact that such data can strongly constrain radiative wind models. In the following, we shall review recent results coming from HARO of active B stars and we shall focus on our radiative wind model for active hot stars which integrates these measurements.

Gas and Dust Emission from the Nuclear Region of the Circinus Galaxy

Simultaneous modeling of the line and continuum emission from the nuclear region of the Circinus galaxy is presented. Composite models that include the combined effect of shocks and photoionization from the active center and from the circumnuclear star-forming region are considered. The effects of dust reradiation, bremsstrahlung from the gas, and synchrotron radiation are treated consistently. Models that fit the continuum energy distribution of Circinus are used to constrain all possible models suitable for the line emission; they are all, together, aimed to converge to a most probable representation of the central emission region of Circinus. The proposed model accounts for two important observational features. First, the high obscuration of Circinus central source is produced by high-velocity and dense clouds with characteristic dust-to-gas ratios above 10-12. Their large velocities, up to 1500 km s-1, place them very close to the active center. Second, the derived size of the line-emitting region (~13 pc) is well in agreement with the observed limits for the coronal (<10 pc) and narrow-line regions (~30 pc) of Circinus.

Spectrophotometric study of four bright Be stars

The spectrophotometric observations of four Be stars and one normal B-type star are reported. The continuum energy distribution data of these stars are presented in the wavelength range of λλ3200–8000 A. The observations are compared with synthetic models to estimate effective temperature and to examine the behaviour of the circumstellar envelope of Be stars on their continuum energy distributions. The excess emission from the envelope affects the continua of the Be stars HR 1786 and HR 1910 strongly in the near-ultraviolet and near-infrared regions.

The Broadband Spectral Energy Distributions of the Cloverleaf Quasar and IRAS F10214+4724

We have constructed broadband spectral energy distributions for the Cloverleaf quasar (z = 2.56) and the luminous infrared galaxy IRAS F10214+4724 (z = 2.28). These are to date the only two high-redshift objects known with measured thermal far-infrared spectra and the only two with solid millimeter-wave detections of molecular gas. The continuum data are assembled from the literature, from a new analysis of IRAS measurements, and from new measurements in the near-infrared, optical, and at 1.25 mm. The spectral shapes and luminosities of the two objects are nearly identical from the rest submillimeter to 20 μm, but they diverge dramatically in the optical/ultraviolet. A simple unifying obscuration/reflection model is presented that may explain the differences. Considering their very similar molecular gas content, together with evidence based on the continuum energy distributions and optical spectropolarimetry, it appears quite plausible that the Cloverleaf and F10214+4724 in fact differ for the most part only in their orientations with respect to Earth.

CONTINUUM ENERGY DISTRIBUTION OF BE STARS IN THE OPTICAL REGION

ABSTRACT The continuum energy distributions of seven Be stars are reported in the wavelength region lambda-lambda 3200-8000A. The observed data are used to derive the effective temperatures of the stars. The discrepancies in the observed energy are discussed.

The early ultraviolet, optical, and radio evolution of the soft X-ray transient GRO J0422+32

We have monitored the evolution of the transient X-ray source GRO J0422+32 from approximately 2 weeks postdiscovery into its early decline phase at ultraviolet, optical, and radio wavelengths. Optical and ultraviolet spectra exhibit numerous, but relatively weak, high-excitation emission lines such as those arising from He II, N III, N V, and C IV superposed on an intrinsically blue continuum. High-resolution optical spectroscopy reveals line profiles which are double peaked, and in the case of the higher order Balmer lines, superposed on a broad absorption profile. The early outburst optical-ultraviolet continuum energy distribution is well represented by a two power-law fit with a break at approximately equal 4000 A. Radio observations with the Very Large Array (VLA) reveal a flat-spectrum source, slowly increasing in intensity at the earliest epochs observed, followed by an approximate power-law decay light curve with an index of -1. Light curves for each wavelength domain are presented and discussed. Notable are the multiple secondary outbursts seen in the optical more than 1 year postdiscovery, and spectral changes associated with secondary rises seen in the radio and UV. We find that the ultraviolet and optical characteristics of GRO J0422+32 as well as its radio evolution, are similar to other recent well-observed soft X-ray transients (also called X-ray novae) such as Cen X-4, A0620-00 (V616 Mon), and Nova Muscae 1991 (GS 1124-683), suggesting that GRO J0422+32 is also a member of that subclass of low-mass X-ray binaries. We present definitive astrometric determination of the source position, and place an upper limit of R approximately equals 20 from our analysis of the Palomar Observatory Sky Survey (POSS). Additionally, we derive distinct values for color excess from analysis of the optical (E(B-V) = 0.23) and ultraviolet (E(B-V) = 0.4) data, suggesting an intrinsic magnitude of 19-19.5 for the progenitor if it is mid-K dwarf. This leads to a likely range of 2.4-3.0 kpc for the source distance, which is consistent with our separate estimate of 2.4 +/- 0.4 kpc based on measurement of the NaD interstellar line profile. Adopting 2.4 kpc and E(B-V) = 0.23, the outburst absolute magnitude was M approximately equals 0.0, which is a typical value for this class of objects.

OPTICAL AND ULTRAVIOLET SPECTROSCOPY OF VW HYDRI

ABSTRACT Spectra of the SU UMa type dwarf nova VW Hydri obtained in the visual (lambda-lambda 3400-7200A) and ultraviolet (lambda-lambda 1150-3200A) spectral regions are presented. During the quiescent phase, visual spectra of VW Hydri present strong double-peaked Balmer emission lines. In addition, He I lambda 5876, Fe II lambda-lambda 4233, 5196 He I lambda 5015, Fe II lambda 5018, He I lambda 4922, Fe II lambda 4293, He II lambda 4686, and He I lambda-lambda 4471, 6678 appear in emission. The S-wave behavior of the hot spot is well defined. The amplitude of the radial velocity curve for H-alpha is 39 (±11) km/s and for H-beta is 85 (±23) km/s. From the radial velocity amplitude and the total line width we derived the primary mass in the range of 0.91 solar mass to 1.28 solar mass and the mass ratio q = M1/M2 = 4.4 to 6.4. We applied the method given by Schoembs and Vogt (1981), which is a modified version of the method described earlier by Warner (1973). We compared and discussed the fundamental physical and spectral parameters with those in the literature. In the ultraviolet region we obtained disk temperatures in the range of 14500-48000 K, using continuum fluxes. The continuum energy distributions were compared with optically thick accretion disk models. In the IUE SWP region the best-fit spectrum is of the form Flambda proportional to lambda -2.4. In this region the effective disk radius is between 0.69Rodot and 0.75Rodot. The mass accretion rate (M) was computed with a relation given by Faulkner (1971), and is about 0-10 Modot yr-1. From the P Cygni profile of the C IV doublet, terminal velocities of about 2250 km/s for a normal outburst and 2500 km/s for superoutburst were derived. Mass loss rates were derived using these velocities as about 0.8 to 6 x 10-13 Modot yr-1 for normal outbursts and about 0.8 to 7 x 10-13 Modot yr-1 for superoutburst.

ROSAT/XRT-PSPC observations and the ionizing continuum of Seyfert 1 galaxy Mrk 478

The ROSAT/XRT-PSPC observations of the Seyfert 1 galaxy Mrk 478 are presented. Together with the optical and ultraviolet spectra of this galaxy, obtained within eight months of the X-ray observations, these new data are used to determine the continuum energy distribution (CED) of Mrk 478, from 1 μm to about 2.0 keV with a small break between 11.3 eV and 0.1 keV. The ultraviolet/soft X-ray CED is similar to the spectrum of a thin accretion disc for both a rotating and a non-rotating black hole, although both models underestimate the flux at energies higher than 0.4 keV. These observations establish that the covering factor of the clouds in the broad-line region in this Seyfert 1 galaxy is about 0.15 and that the energy of the ionizing continuum is similar to the total energy in the broad emission lines. In particular, we find that the observed CED can reproduce the observed line ratios and the luminosity of the Ly α line, indicating that the clouds in the broad-line region see a continuum similar to the observed continuum.

Multiwavelength analysis of quasars, Seyfert galaxies, and starbursts

view Abstract Citations (13) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiwavelength Analysis of Quasars, Seyfert Galaxies, and Starbursts Mas-Hesse, J. Miguel ; Rodriguez-Pascual, Pedro M. ; de Cordoba, L. S. F. ; Mirabel, I. Felix Abstract We have analyzed the multiwavelength (radio to X-ray) properties of a sample of nearly 100 galaxies with different levels of activity: quasi- stellar objects, Seyfert 1 and 2 galaxies, and starburst galaxies. We have tested the implications of "unified Seyfert models," which assume that Seyfert 1 and 2 galaxies are intrinsically similar but seen at different angles through a dense obscuring torus. We have found significant differences between the continuum energy distribution of both Seyfert classes at high energies, with a systematic lack of UV and X-ray (soft and hard) emission in Seyfert 2 compared to Seyfert 1 galaxies. The measured ratios between the emission at various wavelengths differ from the values predicted by the "occultation/reflection" picture. It is necessary to complement this picture with additional energy sources to reconcile it with the observational results. We discuss briefly in this contribution the nature of these sources. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1994 DOI: 10.1086/192022 Bibcode: 1994ApJS...92..599M Keywords: Quasars; Seyfert Galaxies; Spectral Emission; Spectral Energy Distribution; Starburst Galaxies; Infrared Spectra; Ultraviolet Emission; X Ray Spectra; Astronomy; GALAXIES: NUCLEI; GALAXIES: SEYFERT; INFRARED: GALAXIES; ULTRAVIOLET: GALAXIES; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (1) MAST (1)

A model for the continuum energy distribution of the ultraluminous galaxy IRAS Formula

If indeed early type galaxies used up most of their gas to form stars in a time short compared to their collapse time and if a roughly constant fraction of metals is locked up in dust grains, these galaxies may easily become opaque to starlight and emit most of their luminosity in the far-IR. The corresponding spectral energy distribution matches remarkably well the observed continuum spectrum of the ultraluminous galaxy IRAS F$10214+4724$ from UV to sub-mm wavelengths, i.e. over almost four decades in frequency, for a galactic age $\lsim 1\,$Gyr. The bolometric luminosity in this model is $\simeq 2.7\times 10^{14}\Lsol$ ($H_0 =50\,\hbox{km}\,\hbox{s}^{-1} \,\hbox{Mpc}^{-1}$, $\Omega =1$), i.e. somewhat lower than implied by previous models. In the present framework, the bolometric luminosity of the galaxy is expected to decrease by a factor $\gsim 30$ during the subsequent evolution.