scholarly journals Continuum and emission line observations of Wolf-Rayet stars: single and “WR+abs” objects

1995 ◽  
Vol 163 ◽  
pp. 96-104
Author(s):  
Patrick W. Morris
Keyword(s):  
Energy Distribution ◽  
Emission Line ◽  
Absorption Line ◽  
Frequency Distribution ◽  
Power Law ◽  
Line Center ◽  
Continuous Energy ◽  
Important Discrepancy ◽  
The Galaxy ◽  
The Continuum

The UV — IR properties of the continuous energy distribution of single WR stars in the Galaxy and LMC are reviewed. The observed, dereddened distributions may be approximated as a power law Fλ ∼ λ−α with a non-Rayleigh Jeans range of α directly associated with the emission of excess flux over the full wavelength range and across all spectral subtypes. The observational results are compared to published NLTE models, where we find an important discrepancy in the frequency distribution of α for Galactic WN stars. A dependency of emission line equivalent widths on the continuum flux at line center is discussed; the systematic offset of the absorption line (but otherwise presumed single) objects is examined, and the observed behavior is compared to models and explained with simple theory.

scholarly journals Dust Distribution in IRAS Seyfert Galaxies

1994 ◽  
Vol 159 ◽  
pp. 355-355
Author(s):  
M. G. Pastoriza ◽  
Charles Bonatto ◽  
Eduardo Bica ◽  
T. Storchi-Bergmann
Keyword(s):  
Emission Line ◽  
Power Law ◽  
Dust Emission ◽  
Seyfert Galaxies ◽  
Emission Model ◽  
Line Region ◽  
Population Type ◽  
The Galaxy ◽  
Dilution Effects ◽  
Dust Distribution

Observational evidences of dust in the nuclear region of AGNs are substantial (Rudy 1984, ApJ, 284, 33; Jones et al. 1984, PASP, 96, 692). The ionization cones observed in several Seyfert galaxies has been interpreted as shadowing effects by a dust obscuring torus which hides the broad emission line region (BLR) and the central source (Wilson 1992; Storchi-Bergmann, Mulchaey and Wilson 1992, ApJ 395, L73). A large sample of optical and far-IR data for IRAS Seyfert galaxies has been analysed together with dust emission models (Bonatto and Pastoriza 1993), where it has been concluded that the same dust emission model can be applied to both Seyfert types. In order to further study the effects of dust in the spectra of active galactic nuclei, we have obtained spectrophotometry of 21 IRAS Seyfert galaxies in the range 3500–7200 Å and analyse them in conjuction with their IRAS fluxes. The stellar population type is derived from comparisons with normal galaxy templates using dilution effects in the K CaII line as discriminator. For 55% of the sample the population is of late type. For the rest, blue continua due to recent star formation and/or power-law may amount up to 30% at 4000Å. We conclude that the bulge stellar populations of IRAS Seyfert galaxies are similar to those of normal spirals, except that they are more reddened by E(B-V)i ∼ 0.20. Population-subtracted emission line ratios indicate on average stronger reddening for the narrow-line region (E(B-V)l ∼ 0.8. From photoionization models a power-law index for the ionizing continuum α=1.5, and a metallicity larger than solar are obtained. The most luminous IRAS galaxy of the sample (IRAS555) is discuss in detail: in order to be compatible with the observed IRAS fluxes and the optical stellar continuum, the ionizing continuum must be reddened by AV > 10 magnitudes. Consequently a dust structure in this galaxy appears to be increasingly affecting stars and gas towards the galaxy center.

scholarly journals IUE Observations of Novae

1980 ◽  
Vol 5 ◽  
pp. 285-291
Author(s):  
Warren M. Sparks ◽  
Chi-Chao Wu ◽  
Albert V. Holm ◽  
Francis H. Schiffer
Keyword(s):  
Emission Line ◽  
Absorption Line ◽  
Wavelength Range ◽  
Emission Lines ◽  
First Year ◽  
Time Behavior ◽  
International Ultraviolet Explorer ◽  
Ultraviolet Wavelength ◽  
Visual Magnitude ◽  
The Continuum

In addition to offering observing time on a regular schedule, the International Ultraviolet Explorer (IUE) satellite is also being used to observe “targets of opportunity.” Novae represent one of the most exciting targets of opportunity and also one of the most difficult because of their rapid time behavior. During the first year of operation of IUE we were extremely fortunate to have three bright novae outbursts occur: Nova Cygni 1978, WZ Sagittae, and U Scorpii.Nova Cyg 1978, a fast nova, reached a maximum apparent visual magnitude of 6.2 on September 12, 1978 (Slovak and Vogt 1979). Figure 1 shows the relative flux of Nova Cyg 1978 in the long ultraviolet wavelength range (1900-3200Å) at several different times. One day after maximum (Sept. 13), the nova is still in its absorption line phase. At this point it looks like a supergiant F star with mostly Fell absorption lines (also see Cassatella et al. 1979). Later spectra show the emergence of emission lines, which is the characteristic behavior of novae in the visual. Magnesium II at 2800Å is the strongest emission line in this part of the spectrum for at least a month after outburst. The last spectrum (Nov. 1) shows mainly semi-forbidden lines of carbon, nitrogen, and oxygen. It should also be noted that the slope of the continuum flattens as the nova evolves.

scholarly journals Evidence for disks around certain luminous Magellanic cloud stars from the study of FeII

1987 ◽  
Vol 122 ◽  
pp. 443-444
Author(s):  
G. Muratorio ◽  
M. Friedjung
Keyword(s):  
Energy Distribution ◽  
Emission Line ◽  
Line Emission ◽  
Magellanic Cloud ◽  
Emission Lines ◽  
Absorption Lines ◽  
Line Of Sight ◽  
Continuous Energy

Study of FeII emission lines in emission and absorption using both emission line self absorption curves and ultraviolet spectral synthetis, shows that line emission is produced in the case of certain luminous Magellanic Cloud stars, in a region not in front of the photosphere. This region is most easily understood as being a disk. Absorption lines of FeII are either produced by a wind, or if the disk inclination is small with respect to the line of sight, in layers associated with the disk. The presence of disks also helps one to explain the form of the continuous energy distribution.

scholarly journals Absolute Energy Distribution in Rho Cassiopbiae

1977 ◽  
Vol 42 ◽  
pp. 640-640
Author(s):  
S.C. Joshi ◽  
B.S. Rautela
Keyword(s):  
Energy Distribution ◽  
Wavelength Range ◽  
Continuous Energy ◽  
Absolute Energy ◽  
Circumstellar Shell ◽  
The Continuum

AbstractThe continuous energy distribution of ρ Cas obtained in the wavelength range 340 - 710 nm has been compared with the energy distribution of δ CMa in the same wavelength range. The circumstellar shell associated with ρ Cas seems to modify the continuum of the star appreciably. Variations in the Balmer emission of ρ Cas taking place within a day are noticed.

scholarly journals The continuum energy distribution of single galactic Wolf-Rayet stars

1999 ◽  
Vol 193 ◽  
pp. 67-68
Author(s):  
Bas A. den Hond ◽  
Peter S. Conti ◽  
H. Lamers
Keyword(s):  
Energy Distribution ◽  
Power Law ◽  
Continuum Energy ◽  
The Continuum

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.

scholarly journals Gaia-assisted discovery of a detached low-ionisation BAL quasar with very large ejection velocities

2020 ◽  
Vol 634 ◽  
pp. A111 ◽  
Author(s):  
J. P. U. Fynbo ◽  
P. Møller ◽  
K. E. Heintz ◽  
J. N. Burchett ◽  
L. Christensen ◽  
...  
Keyword(s):  
Emission Line ◽  
Absorption Line ◽  
Emission Lines ◽  
Broad Absorption ◽  
Broad Absorption Line ◽  
Red Edge ◽  
First Case ◽  
Bl Lac ◽  
Spatially Extended ◽  
Extended Emission

We report on the discovery of a peculiar broad absorption line (BAL) quasar identified in our Gaia-assisted survey of red quasars. The systemic redshift of this quasar was difficult to establish because of the absence of conspicuous emission lines. Based on deep and broad BAL troughs of at least Si IV, C IV, and Al III, a redshift of z = 2.41 was established under the assumption that the systemic redshift can be inferred from the red edge of the BAL troughs. However, we observe a weak and spatially extended emission line at 4450 Å that is most likely due to Lyman-α emission, which implies a systemic redshift of z = 2.66 if correctly identified. There is also evidence for the onset of Lyman-α forest absorption bluewards of 4450 Å and evidence for Hα emission in the K band consistent with a systemic redshift of z = 2.66. If this redshift is correct, the quasar is an extreme example of a detached low-ionisation BAL quasar. The BALs must originate from material moving with very large velocities ranging from 22 000 km s−1 to 40 000 km s−1. To our knowledge, this is the first case of a systemic-redshift measurement based on extended Lyman-α emission for a BAL quasar. This method could also be useful in cases of sufficiently distant BL Lac quasars without systemic-redshift information.

Evolution of the number of communicative civilizations in the Galaxy: implications on Fermi paradox

2020 ◽  
Vol 19 (4) ◽  
pp. 314-319
Author(s):  
Giorgio Spada ◽  
Daniele Melini
Keyword(s):  
Power Law ◽  
Slow Rate ◽  
Rate Of Growth ◽  
Long Run ◽  
Rate Of Increase ◽  
The Galaxy ◽  
Zero Number

AbstractIt has been recently proposed DeVito [(2019) On the meaning of Fermi's paradox. Futures, 389–414] that a minimal number of contacts with alien radio-communicative civilizations could be justified by their logarithmically slow rate of growth in the Galaxy. Here we further develop this approach to the Fermi paradox, with the purpose of expanding the ensemble of the possible styles of growth that are consistent with the hypothesis of a minimal number of contacts. Generalizing the approach in DeVito (2019), we show that a logarithmic style of growth is still found. We also find that a style of growth following a power law would be admissible, however characterized by an exponent less than one, hence describing a sublinear increase in the number of communicative civilizations, still qualitatively in agreement with DeVito (2019). No solutions are found indicating a superlinear increase in the number of communicative civilizations, following for example an exponentially diverging law, which would cause, in the long run, an unsustainable proliferation. Although largely speculative, our findings corroborate the idea that a sublinear rate of increase in the number of communicative civilizations in the Galaxy could constitute a further resolution of Fermi paradox, implying a constant and minimal – but not zero – number of contacts.

Ionized gas kinematics and luminosity profiles of Low-z Lyman Alpha Blobs

2019 ◽  
Vol 15 (S359) ◽  
pp. 413-414
Author(s):  
María P. Agüero ◽  
Rubén Díaz ◽  
Mischa Schirmer
Keyword(s):  
Emission Line ◽  
Galactic Nuclei ◽  
Host Galaxies ◽  
Ionized Gas ◽  
Lyman Alpha ◽  
Gas Kinematics ◽  
The Universe ◽  
Very High ◽  
The Continuum

AbstractThis work is focused on the characterization of the Seyfert-2 galaxies hosting very large, ultra-luminous narrow-line regions (NLRs) at redshifts z = 0.2−0.34. With a space density of 4.4 Gcp−3 at z ∼ 0.3, these “Low Redshift Lyman-α Blob” (LAB) host galaxies are amongst the rarest objects in the universe, and represent an exceptional and short-lived phenomenon in the life cycle of active galactic nuclei (AGNs). We present the study of GMOS spectra for 13 LAB galaxies covering the rest frame spectral range 3700–6700 Å. Predominantly, the [OIII]λ5007 emission line radial distribution is as widespread as that of the continuum one. The emission line profiles exhibit FWHM between 300–700 Km s−1. In 7 of 13 cases a broad kinematical component is detected with FWHM within the range 600–1100 Km s−1. The exceptionally high [OIII]λ5007 luminosity is responsible for very high equivalent width reaching 1500 Å at the nucleus.

scholarly journals Blocks Size Frequency Distribution in the Enceladus Tiger Stripes Area: Implications on Their Formative Processes

Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 82
Author(s):  
Maurizio Pajola ◽  
Alice Lucchetti ◽  
Lara Senter ◽  
Gabriele Cremonese
Keyword(s):  
Frequency Distribution ◽  
Power Law ◽  
Size Frequency Distribution ◽  
Surface Stresses ◽  
Size Frequency ◽  
The One ◽  
Power Law Index ◽  
Comet 67P ◽  
South Polar ◽  
Degree Of Fragmentation

We study the size frequency distribution of the blocks located in the deeply fractured, geologically active Enceladus South Polar Terrain with the aim to suggest their formative mechanisms. Through the Cassini ISS images, we identify ~17,000 blocks with sizes ranging from ~25 m to 366 m, and located at different distances from the Damascus, Baghdad and Cairo Sulci. On all counts and for both Damascus and Baghdad cases, the power-law fitting curve has an index that is similar to the one obtained on the deeply fractured, actively sublimating Hathor cliff on comet 67P/Churyumov-Gerasimenko, where several non-dislodged blocks are observed. This suggests that as for 67P, sublimation and surface stresses favor similar fractures development in the Enceladus icy matrix, hence resulting in comparable block disaggregation. A steeper power-law index for Cairo counts may suggest a higher degree of fragmentation, which could be the result of localized, stronger tectonic disruption of lithospheric ice. Eventually, we show that the smallest blocks identified are located from tens of m to 20–25 km from the Sulci fissures, while the largest blocks are found closer to the tiger stripes. This result supports the ejection hypothesis mechanism as the possible source of blocks.

scholarly journals Emerge: Empirical predictions of galaxy merger rates since z ∼ 6

2020 ◽  
Author(s):  
Joseph A O’Leary ◽  
Benjamin P Moster ◽  
Thorsten Naab ◽  
Rachel S Somerville
Keyword(s):  
Galaxy Formation ◽  
Power Law ◽  
Stellar Mass ◽  
Direct Result ◽  
Mass Relation ◽  
Massive Galaxies ◽  
The Galaxy ◽  
Major Merger ◽  
Low Mass ◽  
Merger Rate

Abstract We explore the galaxy-galaxy merger rate with the empirical model for galaxy formation, emerge. On average, we find that between 2 per cent and 20 per cent of massive galaxies (log10(m*/M⊙) ≥ 10.3) will experience a major merger per Gyr. Our model predicts galaxy merger rates that do not scale as a power-law with redshift when selected by descendant stellar mass, and exhibit a clear stellar mass and mass-ratio dependence. Specifically, major mergers are more frequent at high masses and at low redshift. We show mergers are significant for the stellar mass growth of galaxies log10(m*/M⊙) ≳ 11.0. For the most massive galaxies major mergers dominate the accreted mass fraction, contributing as much as 90 per cent of the total accreted stellar mass. We reinforce that these phenomena are a direct result of the stellar-to-halo mass relation, which results in massive galaxies having a higher likelihood of experiencing major mergers than low mass galaxies. Our model produces a galaxy pair fraction consistent with recent observations, exhibiting a form best described by a power-law exponential function. Translating these pair fractions into merger rates results in an inaccurate prediction compared to the model intrinsic values when using published observation timescales. We find the pair fraction can be well mapped to the intrinsic merger rate by adopting an observation timescale that decreases linearly with redshift as Tobs = −0.36(1 + z) + 2.39 [Gyr], assuming all observed pairs merge by z = 0.

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