scholarly journals Observations of PKS 2155–304 with the Extreme Ultraviolet Explorer

1994 ◽  
Vol 159 ◽  
pp. 322-322
Author(s):  
A. Fruscione ◽  
C.S. Bowyer ◽  
T.E. Carone ◽  
S.M. Kahn ◽  
A. Königl ◽  
...  
Keyword(s):  
Light Curve ◽  
Spectroscopic Data ◽  
Extreme Ultraviolet ◽  
High Accuracy ◽  
Bl Lac ◽  
Deep Survey

We have studied the first extreme ultraviolet spectroscopic data and a high accuracy light curve for the BL Lac object PKS 2155–304 observed with the Extreme Ultraviolet Explorer (EUVE) on July 21–22, 1992. This target was observed with the Deep Survey Spectrometer telescope for approximateley 30,000 sec during the in-orbit-calibration phase of the mission, allowing to obtain simultaneous image and spectrum.

scholarly journals ‘Sumer’ – Solar Ultraviolet Measurements of Emitted Radiation

1994 ◽  
Vol 144 ◽  
pp. 619-624 ◽  
Author(s):  
K. Wilhelm ◽  
W. Curdt ◽  
A. H. Gabriel ◽  
M. Grewing ◽  
M. C. E. Huber ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Extreme Ultraviolet ◽  
Flow Characteristics ◽  
Magnetic Activity ◽  
High Accuracy ◽  
The Sun ◽  
Lower Corona ◽  
Doppler Shifts ◽  
Solar Magnetic Activity ◽  
Solar Ultraviolet

AbstractThe experiment Solar Ultraviolet Measurements of Emitted Radiation (SUMER) is designed for the investigations of plasma flow characteristics, turbulence and wave motions, plasma densities and temperatures, structures and events associated with solar magnetic activity in the chromosphere, the transition zone and the corona. Specifically, SUMER will measure profiles and intensities of extreme ultraviolet (EUV) lines emitted in the solar atmosphere ranging from the upper chromosphere to the lower corona; determine line broadenings, spectral positions and Doppler shifts with high accuracy; provide stigmatic images of selected areas of the Sun in the EUV with high spatial, temporal and spectral resolution and obtain full images of the Sun and the inner corona in selectable EUV lines, corresponding to a temperature range from 104to more than 1.8 x 106K. The spatial and spectral resolution capabilities of the instrument will be considered in this contribution in some detail, and a new detector concept will be introduced.

scholarly journals The Subdwarf Eclipsing Binary LB3459 (AA Dor)

1982 ◽  
Vol 69 ◽  
pp. 455-456
Author(s):  
R.W. Hilditch ◽  
Graham Hill ◽  
D. Kilkenny
Keyword(s):  
Light Curve ◽  
Observational Data ◽  
Spectroscopic Data ◽  
Main Sequence ◽  
Primary Component ◽  
Curve Analysis ◽  
Current Status ◽  
Evolutionary Models ◽  
Light Curve Analysis ◽  
Normal Composition

A review was presented of the currently available observational data on this evolved system, namely, uvby photometry (Kilkenny et al. 1978; paper II) radial velocities (Kilkenny et al. 1981; paper III) and a non-LTE atmosphere analysis of the primary component (Kudritski et al. 1981). Kudritski et al. conclude that T(pr) = 40000 ± 2500°K and log g = 5.3 ± 0.2 and from the spectroscopic data and light curve analysis (papers II, III) derive masses and radii for the primary and secondary components of M(pr) ≃ 0.25 M⊙, M(sec) ≃ 0.04 M⊙, R(pr) ≃ 0.16R⊙, R(sec) ≃ 0.09R⊙ respectively. Thus the primary component is a normal sd0 star whilst the secondary component is a most enigmatic object, perhaps a normal composition degenerate dwarf but of too low a mass to be on the main sequence, perhaps an evolved degenerate object but then the radius is too large. The published evolutionary models for this system (Paczynski 1980; Conti et al 1981) do not adequately describe its current status.

scholarly journals A high resolution line list for AlO

2021 ◽  
Author(s):  
Charles A Bowesman ◽  
Meiyin Shuai ◽  
Sergei N Yurchenko ◽  
Jonathan Tennyson
Keyword(s):  
High Resolution ◽  
Spectroscopic Data ◽  
Vibrational Energy ◽  
Energy Levels ◽  
Laboratory Data ◽  
High Accuracy ◽  
High Resolution Spectroscopy ◽  
Line List ◽  
Vibrational Energy Levels

Abstract Indications of aluminium monoxide in atmospheres of exoplanets are being reported. Studies using high resolution spectroscopy should allow a strong detection but require high accuracy laboratory data. A Marvel (measured active rotational-vibrational energy levels) analysis is performed for the available spectroscopic data on 27Al16O: 22 473 validated transitions are used to determine 6 485 distinct energy levels. These empirical energy levels are used to provide an improved, spectroscopically accurate version of the ExoMol ATP line list for 27Al16O; at the same time the accuracy of the line lists for the isotopically-substituted species 26Al16O, 27Al17O and 27Al18O are improved by correcting levels in line with the corrections used for 27Al16O. These line lists are available from the ExoMol database at http://www.exomol.com.

scholarly journals Preflare very long-periodic pulsations observed in Hα emission before the onset of a solar flare

2020 ◽  
Vol 639 ◽  
pp. L5
Author(s):  
Dong Li ◽  
Song Feng ◽  
Wei Su ◽  
Yu Huang
Keyword(s):  
Solar Flare ◽  
Light Curve ◽  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Light Curves ◽  
Trigger Mechanism ◽  
X Ray ◽  
Hα Emission ◽  
Plasma Loop ◽  
Full Disk

Context. Very long-periodic pulsations during preflare phases (preflare-VLPs) have been detected in the full-disk solar soft X-ray (SXR) flux. They may be regarded as precursors to solar flares and may help us better understand the trigger mechanism of solar flares. Aims. In this Letter, we report a preflare-VLP event prior to the onset of an M1.1 circular-ribbon flare on 2015 October 16. It was simultaneously observed in Hα, SXR, and extreme ultraviolet (EUV) wavelengths. Methods. The SXR fluxes in 1−8 Å and 1−70 Å were recorded by the Geostationary Operational Environmental Satellite (GOES) and Extreme Ultraviolet Variability Experiment, respectively; the light curves in Hα and EUV 211 Å were integrated over a small local region, which were measured by the 1 m New Vacuum Solar Telescope and the Atmospheric Imaging Assembly (AIA), respectively. The preflare-VLP is identified as the repeat and quasi-periodic pulses in light curves during preflare phase. The quasi-periodicity can be determined from the Fourier power spectrum with Markov chain Monte Carlo-based Bayesian. Results. Seven well-developed pulses are found before the onset of an M1.1 circular-ribbon flare. They are firstly seen in the local light curve in Hα emission and then discovered in full-disk SXR fluxes in GOES 1−8 Å and ESP 1−70 Å, as well as the local light curve in AIA 211 Å. These well-developed pulses can be regarded as the preflare-VLP, which might be modulated by LRC-circuit oscillation in the current-carrying plasma loop. The quasi-period is estimated to be ∼9.3 min. Conclusions. We present the first report of a preflare-VLP event in the local Hα line and EUV wavelength, which could be considered a precursor of a solar flare. This finding should therefore prove useful for the prediction of solar flares, especially for powerful flares.

scholarly journals Observations of AGN with the Extreme Ultraviolet Explorer

1994 ◽  
Vol 159 ◽  
pp. 105-110
Author(s):  
Herman L. Marshall
Keyword(s):  
Power Law ◽  
Extreme Ultraviolet ◽  
Active Galaxies ◽  
Spectral Features ◽  
Bl Lac Objects ◽  
X Ray ◽  
Difficult Time ◽  
Bl Lac ◽  
First Results ◽  
Galactic Sources

The first results from surveys performed in the extreme ultraviolet (EUV) will be described in the context of studies of active galaxies and BL Lac objects. About a dozen extra-galactic sources are known so far to emit sufficient EUV radiation that they are detectable even through the Galactic interstellar medium. These results are interpreted in the context of a model of EUV or soft X-ray excesses in the case of AGN. In the case of BL Lac objects, the detections indicate that the steep soft X-ray power law spectra continue into the EUV and that there is little intrinsic gas. Finally, there now exists EUV spectra from the Extreme Ultraviolet Explorer for one BL Lac, PKS 2155-304 and two AGN: Mk 478 and NGC 5548. The spectra show no significant spectral features; for AGN, it indicates that optically thin and emission line models may have a difficult time explaining the EUV and soft X-ray bumps.

scholarly journals A Large, Deep Survey of the Taurus Dark Clouds

2003 ◽  
Vol 211 ◽  
pp. 79-80
Author(s):  
S. L. Osborne ◽  
R. F. Jameson ◽  
P. D. Dobbie ◽  
E. L. Martín
Keyword(s):  
Spectroscopic Data ◽  
Brown Dwarfs ◽  
Theoretical Models ◽  
Late Type ◽  
M Dwarfs ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Deep Survey ◽  
Hα Emission

Preliminary results from a deep R, I and Z band survey of ~ 6 square degrees of the Taurus Dark Cloud region are presented. 186 potential brown dwarfs have been unearthed, with seven having follow-up spectroscopic data. The spectra reveal three mid/late-type M dwarfs, of which two show weak Hα emission. If these objects are members of the TDC region, theoretical models suggest masses in the range 10 – 20 MJ.

scholarly journals The Thermal Pressure of the Interstellar Medium Derived from Cloud Shadows in the Extreme Ultraviolet

1997 ◽  
Vol 166 ◽  
pp. 61-64 ◽  
Author(s):  
Thomas W. Berghöfer ◽  
Stuart Bowyer ◽  
Richard Lieu ◽  
Jens Knude
Keyword(s):  
Interstellar Medium ◽  
Extreme Ultraviolet ◽  
Optical Data ◽  
Interstellar Gas ◽  
Thermal Pressure ◽  
Deep Survey ◽  
X Ray Background ◽  
Almost All ◽  
New Evidence ◽  
Local Cloud

AbstractWe have used the Deep Survey telescope of EUVE to investigate shadows in the diffuse EUV/Soft X-ray background cast by clouds in the interstellar medium. We confirm the existence of a shadow previously reported, and provide evidence for two new shadows. We used IRAS data to identify the clouds producing these shadows and to determine their optical depth to EUV radiation. The EUV-absorbing clouds are optically thick in the EUV, and all EUV emission detected in the direction of these shadows must be produced from material in front of the clouds. We obtained new optical data to determine the distance to these clouds. We use a new differential cloud technique to obtain the pressure of the interstellar medium. These results do not depend on any zero level calibration of the data. Our results provide evidence that the pressure of the hot interstellar gas is the same in three different directions in the local interstellar medium, and is at least 8 times higher than derived for the local cloud surrounding our Sun. This provides new evidence for large thermal pressure imbalances in the local ISM, and directly contradicts the basic assumption of thermal pressure equilibrium used in almost all present models of the interstellar medium.

scholarly journals The origin of R CrA variability

2019 ◽  
Vol 630 ◽  
pp. A132 ◽  
Author(s):  
E. Sissa ◽  
R. Gratton ◽  
J. M. Alcalà ◽  
S. Desidera ◽  
S. Messina ◽  
...  
Keyword(s):  
Light Curve ◽  
Spectroscopic Data ◽  
Near Infrared ◽  
Progressive Increase ◽  
Emission Lines ◽  
Periodic Modulation ◽  
Star Forming ◽  
Stable Period ◽  
Total Luminosity ◽  
M Dwarf

Context. R CrA is the brightest member of the Coronet star-forming region and is the closest Herbig AeBe star with a spectrum dominated by emission lines. Its luminosity has been monitored since the end of the nineteenth century, but the origin of its variability, which shows a stable period of 65.767 ± 0.007 days, is still unknown. Aims. We studied photometric and spectroscopic data for this star to investigate the nature of the variability of R CrA. Methods. We exploited the fact that the near-infrared luminosity of the Herbig AeBe stars is roughly proportional to the total luminosity of the stars to derive the absorption, and then mass and age of R CrA. In addition, we modeled the periodic modulation of the light curve as due to partial attenuation of a central binary by a circumbinary disk. This model reproduces the observations very well. Results. We found that the central object in R CrA is a very young (1.5 ± 1.5 Myr) highly absorbed (AV = 5.47 ± 0.4 mag) binary; we obtain masses of MA = 3.02 ± 0.43 M⊙ and MB = 2.32 ± 0.35 M⊙ for the two components. We propose that the secular decrease of the apparent luminosity of R CrA is due to a progressive increase of the disk absorption. This might be related to precession of a slightly inclined disk caused by the recently discovered M-dwarf companion. This means that R CrA might be a triple system hosting a disk.

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