scholarly journals A Study of the Extragalactic UV Radiation in Helix Nebula using GALEX

2021 ◽  
Vol 18 (18) ◽  
Author(s):  
Lakshmi S BOSE
Keyword(s):  
Galaxy Evolution ◽  
Uv Radiation ◽  
Absolute Magnitude ◽  
Photometric Method ◽  
Zodiacal Light ◽  
Uv Emission ◽  
Near Ultraviolet ◽  
Diffuse Background ◽  
Distinct Source ◽  
Flux Measurements

We have studied the ultraviolet sources using Galaxy Evolution Explorer medium imaging surveys in Helix Nebula and estimated UV fluxes by using aperture photometry in distant and near ultraviolet bands. The aperture photometric method produces reliable, accurate flux measurements and found inconsistent with the merged catalog of Galaxy Evolution Explorer. From the current results, the fluxes are consistent with brighter absolute magnitude up to 24.5 and the measurement error increases gradually to more than 50 % at the fainter magnitude side. Percentage of error in far UV is greater than near UV, due to the fact that brighter galaxies are more visible than the near UV sources. The diffuse UV contributors of zodiacal light, airglow contribution in the nebula were estimated. The total extragalactic UV radiation from the detected sources to the diffuse background in the nebula is of the order of 50 ± 14 photons cm-2sr-1s-1Å-1 in NUV band and 28 ±10 photons cm-2sr-1s-1Å-1 in FUV band. HIGHLIGHTS GALEX observations have the potential to find extragalactic UV sources Helix Nebula is first identified for distinct source detection Aperture photometric method can detect fainter sources up to the magnitude of 27 Extragalactic sources in the Helix nebula contribute to diffuse UV emission in the nebula GRAPHICAL ABSTRACT

1.1.8 Photometry of the Zodiacal Light with the Balloon – Borne Telescope Thisbe

1976 ◽  
Vol 31 ◽  
pp. 52-52
Author(s):  
A. Frey ◽  
W. Hofmann ◽  
D. Lemke ◽  
C. Thum
Keyword(s):  
Spectral Range ◽  
No Reduction ◽  
Intensity Increase ◽  
The Sun ◽  
Atmospheric Ozone ◽  
Zodiacal Light ◽  
Reduction Procedure ◽  
Strong Intensity ◽  
Near Ultraviolet ◽  
Upper Limit

We report on new measurements extending the spectral range of our earlier photometry (Frey et al. 1974) to the near ultraviolet. The residual extinction caused by atmospheric ozone was found to be 0.m25 ± 0.m13 (2950 Å) and 0m36 ± 0m13 (2150 Å) at 41.5 km float altitude. Within the errors of 10-30% arising from calibration and the reduction procedure our measurements at 5000, 3450, and 2950 Å are compatible to a colour of the zodiacal light not different from that of the sun. Our result obtained at 2150 Å is an upper limit, since no reduction of airglow and integrated starlight has been done yet at that wavelength. This upper limit is 30% above a solar-like spectrum. This result is not in contradiction to the 0A0-2 measurements (Lillie 1972). The strong intensity increase he found occurs at wavelengths below 2150 Å.

scholarly journals GALEX absolute calibration and extinction coefficients based on white dwarfs

2019 ◽  
Vol 489 (4) ◽  
pp. 5046-5052 ◽  
Author(s):  
Renae E Wall ◽  
Mukremin Kilic ◽  
P Bergeron ◽  
B Rolland ◽  
C Genest-Beaulieu ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
White Dwarfs ◽  
Signal To Noise Ratio ◽  
Model Atmosphere ◽  
Absolute Calibration ◽  
High Signal ◽  
Extinction Coefficients ◽  
Near Ultraviolet ◽  
The Galaxy ◽  
Far Ultraviolet

ABSTRACT We use 1837 DA white dwarfs with high signal-to-noise ratio spectra and Gaia parallaxes to verify the absolute calibration and extinction coefficients for the Galaxy Evolution Explorer (GALEX). We use white dwarfs within 100 pc to verify the linearity correction to the GALEX data. We find that the linearity correction is valid for magnitudes brighter than 15.95 and 16.95 for the far-ultraviolet (FUV) and near-ultraviolet (NUV) bands, respectively. We also use DA white dwarfs beyond 250 pc to calculate extinction coefficients in the FUV and NUV bands: RFUV = 8.01 ± 0.07 and RNUV = 6.72 ± 0.04. These are consistent with the predicted extinction coefficients for Milky Way-type dust in the FUV, but smaller than predictions in the NUV. With well understood optical spectra and state-of-the-art model atmosphere analysis, these white dwarfs currently provide the best constraints on the extinction coefficients for the GALEX data.

Difference in Self-Absorption Effect Compensations Between Power-Spectral Method and Photometric Method for the Luminous Flux Measurements

2016 ◽  
Vol 53 (10) ◽  
pp. 101204
Author(s):  
刘向远 Liu Xiangyuan ◽  
张穗萌 Zhang Suimeng ◽  
徐文清 Xu Wenqing ◽  
范传宇 Fan Chuanyu ◽  
王锦 Wang Jin
Keyword(s):  
Spectral Method ◽  
Luminous Flux ◽  
Photometric Method ◽  
Absorption Effect ◽  
Power Spectral ◽  
Flux Measurements

scholarly journals A Swift view of X-ray and UV radiation in the planet-forming T Tauri system PDS 70

2019 ◽  
Vol 491 (1) ◽  
pp. L56-L60 ◽  
Author(s):  
Simon R G Joyce ◽  
John P Pye ◽  
Jonathan D Nichols ◽  
Kim L Page ◽  
Richard Alexander ◽  
...  
Keyword(s):  
Uv Radiation ◽  
Uv Detection ◽  
Coronal Emission ◽  
X Ray ◽  
Saturation Limit ◽  
Uv Emission ◽  
T Tauri ◽  
Data Release ◽  
Disc Material ◽  
Rotating Star

ABSTRACT PDS 70 is a ∼5-Myr-old star with a gas and dust disc in which several protoplanets have been discovered. We present the first ultraviolet (UV) detection of the system along with X-ray observations taken with the Neil Gehrels Swift Observatory satellite. PDS 70 has an X-ray flux of 3.4 × 10−13 erg cm−2 s−1 in the 0.3–10.0 keV range, and UV flux (U band) of 3.5 × 10−13 erg cm−2 s−1 . At the distance of 113.4 pc determined from Gaia Data Release 2, this gives luminosities of 5.2 × 1029 and 5.4 × 1029 erg s−1, respectively. The X-ray luminosity is consistent with coronal emission from a rapidly rotating star close to the log $\frac{L_{\mathrm{X}}}{L_{\mathrm{bol}}} \sim -3$ saturation limit. We find the UV luminosity is much lower than would be expected if the star were still accreting disc material and suggest that the observed UV emission is coronal in origin.

scholarly journals The UV Upturn in Elliptical Galaxies

1995 ◽  
Vol 164 ◽  
pp. 239-248
Author(s):  
H.C. Ferguson
Keyword(s):  
Galaxy Evolution ◽  
Open Cluster ◽  
Elliptical Galaxies ◽  
Asymptotic Giant Branch ◽  
Star Mass ◽  
Uv Emission ◽  
Stellar Component ◽  
Red Clump ◽  
Ehb Stars ◽  
Uv Upturn

The hot stellar component in elliptical galaxies offers clues to both stellar evolution and galaxy evolution. Current observations suggest that extreme horizontal branch (EHB) stars dominate the far-UV emission from galaxies with the strongest “UV upturns,” while post asymptotic giant branch (PAGB) stars are probably significant contributors for weaker galaxies. Spectra near the Lyman limit indicate that a rather narrow range of temperature (and hence EHB star mass) is required. However, other arguments suggest that most of the helium-burning stars in elliptical galaxies are in the red clump. The HB star mass distribution therefore appears to be strongly bimodal. Such bimodality is qualitatively reproduced by two radically different stellar population models, (those of Lee and Bressan et al.), both of which require that the galaxies be very old. However, the Galactic open cluster NGC 6791 also contains EHB stars and exhibits strong bimodality, indicating that old age may not necessarily be a requirement for the UV upturn phenomenon.

scholarly journals Predicting star formation properties of galaxies using deep learning

2020 ◽  
Vol 493 (4) ◽  
pp. 4808-4815
Author(s):  
Shraddha Surana ◽  
Yogesh Wadadekar ◽  
Omkar Bait ◽  
Hrushikesh Bhosale
Keyword(s):  
Deep Learning ◽  
Star Formation ◽  
Galaxy Evolution ◽  
Formation Rate ◽  
Mass Star ◽  
Learning Techniques ◽  
Alternative Approach ◽  
Star Formation In Galaxies ◽  
Flux Measurements ◽  
Best Fitting

ABSTRACT Understanding the star formation properties of galaxies as a function of cosmic epoch is a critical exercise in studies of galaxy evolution. Traditionally, stellar population synthesis (SPS) models have been used to obtain best-fitting parameters that characterize star formation in galaxies. As multiband flux measurements become available for thousands of galaxies, an alternative approach to characterizing star formation using machine learning becomes feasible. In this work, we present the use of deep learning techniques to predict three important star formation properties – stellar mass, star formation rate, and dust luminosity. We characterize the performance of our deep learning models through comparisons with outputs from a standard SPS code.

scholarly journals The Extragalactic Diffuse Background in the Far Ultraviolet

1990 ◽  
Vol 139 ◽  
pp. 307-316
Author(s):  
Francesco Paresce
Keyword(s):  
Line Of Sight ◽  
Small Scale ◽  
Zodiacal Light ◽  
Dust Layer ◽  
High Ionization ◽  
Spatial Fluctuations ◽  
Diffuse Background ◽  
Far Ultraviolet ◽  
Near Future ◽  
Uv Range

Due mainly to the minimal contaminating effects of zodiacal light and direct stellar emission, the far UV wavelength band from 912 to à 2000 å is ideally suited, in principle at least, for an accurate measurement of a diffuse background component due to sources outside our own galaxy. The cosmological significance of such radiation is of great current interest as it certainly includes the cumulative line-of-sight effect of galaxies and quasars and may include emission from both a lukewarm intergalactic medium and decaying massive particles such as neutrinos, photinos, etc. The radiation required to maintain the IGM at its known high ionization level should also, in any case, appear clearly in this band due to redshift and lookback time effects, thereby providing a crucial clue as to its presently obscure origins. Just how accurately this component can be measured in practice, however, clearly depends on how well we understand the probably dominant galactic component from which it must be disentangled in one way or another except, possibly, at the galactic poles. The residual emission there in this band is on the order of a few ×102 photons cm−2 s−1 sr−1 å−1, of which perhaps as many as 50 units are almost certainly due to galaxies since the small-scale spatial fluctuations corresponding to this flux almost exactly mimic those expected from the known spatial distribution of galaxies. The rest must come from a presently uncertain source, most likely a residual tenuous dust layer at the galactic poles. This latter possibility is at least consistent with recent IRAS results on the diffuse IR background at 100 μm and very sensitive HI, 21 cm measurements in these regions, but an extragalactic origin cannot be presently ruled out. Higher spatial and spectral resolution observations throughout the entire far UV range planned for the near future from orbiting platforms are expected to resolve this last but critically important issue.

AGB and RGB stars in the dwarf irregular galaxy Leo A

2021 ◽  
Vol 647 ◽  
pp. A170
Author(s):  
Alina Leščinskaitė ◽  
Rima Stonkutė ◽  
Vladas Vansevičius
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Near Infrared ◽  
Dwarf Galaxy ◽  
Asymptotic Giant Branch ◽  
Star Formation History ◽  
Photometric Method ◽  
Agb Stars ◽  
Irregular Galaxy ◽  
Red Giant

Context. Leo A is a gas-rich dwarf irregular galaxy of low stellar mass located in the outskirts of the Local Group. It has an extended star formation history with stellar populations spanning a wide age range (∼0.01−10 Gyr). As Leo A is a well-isolated dwarf galaxy, it is a perfect target to study a galactic structure formed entirely by processes of self-induced star formation. Aims. Our aim is to study populations of the brightest asymptotic giant branch (AGB) stars and red giant branch (RGB) stars over the entire extent of the Leo A galaxy. Methods. We analysed populations of AGB and RGB stars in the Leo A galaxy using multicolour photometry data obtained with the Subaru Suprime-Cam (B, V, R, I, Hα) and HST ACS (F475W, F814W) cameras. In order to separate the Milky Way and Leo A populations of red stars, we developed a photometric method that enabled us to study the spatial distribution of AGB and RGB stars within the Leo A galaxy. Results. We found a previously unknown sequence of 26 peculiar RGB stars which probably have a strong CN band in their spectra (∼380−390 nm). This conclusion is supported by the infrared CN spectral features observed in four of these stars with available spectra from the literature. Additionally, we present a catalogue of 32 luminous AGB stars and 3 candidate AGB stars. Twelve AGB stars (three of them might have dusty envelopes) from this sample are newly identified; the remaining 20 AGB stars were already presented in the literature based on near-infrared observations. By splitting the RGB sequence into blue and red parts, we revealed different spatial distributions of the two subsets, with the former being more centrally concentrated than the latter. Cross-identification with spectroscopic data available in the literature suggests that the bulk of blue and red RGB stars are, on average, similar in metallicity; however, the red RGB stars might have an excess of metal-deficient stars of [Fe/H] < −1.8. We also found that the distributions of luminous AGB and blue RGB stars have nearly equal scale lengths (0.′87 ± 0.′06 and 0.′89 ± 0.′09, respectively), indicating that they could belong to the same generation. This conclusion is strengthened by the similarities of the cumulative distributions of AGB and blue RGB stars, both showing more centrally concentrated populations compared to red RGB stars. There is also a prominent decline in the ratio of AGB to RGB stars with an increasing radius. These results suggest that the star-forming disk of Leo A is shrinking, which is in agreement with the outside-in star formation scenario of dwarf galaxy evolution.

scholarly journals Young stars in nearby early-type galaxies: SED fitting based on ultraviolet (UV) and optical imaging

2011 ◽  
Vol 7 (S284) ◽  
pp. 240-243
Author(s):  
Hyunjin Jeong ◽  
Sukyoung K. Yi ◽  
Martin Bureau ◽  
Roger L. Davies
Keyword(s):  
Star Formation ◽  
Optical Imaging ◽  
Galaxy Evolution ◽  
Mass Fraction ◽  
Star Formation History ◽  
Optical Data ◽  
Early Type ◽  
Low Velocity ◽  
Near Ultraviolet ◽  
Order Of Magnitude

AbstractRecent studies from the Galaxy Evolution Explore (GALEX) ultraviolet (UV) data have demonstrated that the recent star formation is more common in early-type galaxies (ETGs) than we used to believe. The UV is one order of magnitude more sensitive than the optical to the presence of young stellar populations. The near-ultraviolet (NUV) lights of ETGs, especially, are used to reveal their residual star formation history. Here we used the GALEX UV data of 34 nearby early-type galaxies from the SAURON sample, all of which have optical data from MDM Observatory. At least 15% of the galaxies in this sample show blue UV-optical colours suggesting recent star formation (Jeong et al. 2009). These NUV blue galaxies are generally low velocity dispersion systems and change the slopes of scaling relations (colour-magnitude relations and fundamental planes) and increase the scatters. To quantify the amount of recent star formation in our sample, we assume two bursts of star formation, allowing us to constrain the age and mass fraction of the young component pixel by pixel (Jeong et al. 2007). The pixel-by-pixel SED fitting based on UV and optical imaging reveals that the mass fraction of young (< 1 Gyr old) stars in ETGs varies between 1 and 3% in the nearby universe (Jeong et al. in prep.). We will compare our results with the prediction from the hierarchical merger paradigm to understand the mechanism of low-level recent star formation observed in early-type galaxies.

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