| 6411. |
- Bengtsson, Hans, et al.
(author)
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V2331 Cygni is an Algol Variable With Deep Eclipses
- 2013
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In: The Journal of the American Association of Variable Star Observers. - 2380-3606. ; 41:2, s. 264-266
-
Journal article (peer-reviewed)abstract
- We report the discovery that V2331 Cygni is not an L star but an eclipsing variable with deep minima, and present a determination of the elements of the star: Epoch = HJD 2456184.296 ±0.001 and Period = 1.3886 ± 0.0001 days.
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| 6412. |
- Bengtsson, Ingemar, 1957-
(author)
-
The Hawking energy on photon surfaces
- 2020
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In: General Relativity and Gravitation. - : Springer Science and Business Media LLC. - 0001-7701 .- 1572-9532. ; 52:5
-
Journal article (peer-reviewed)abstract
- The Hawking energy has a monotonicity property under the inverse mean curvature flow on totally umbilic hypersurfaces with constant scalar curvature in Einstein spaces. It grows if the hypersurface is spacelike, and decreases if it is timelike. Timelike examples include Minkowski and de Sitter hyperboloids, and photon surfaces in Schwarzschild.
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| 6413. |
- Bennert, Vardha N., et al.
(author)
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A Local Baseline of the Black Hole Mass Scaling Relations for Active Galaxies. IV. Correlations Between M (BH) and Host Galaxy sigma, Stellar Mass, and Luminosity
- 2021
-
In: Astrophysical Journal. - : IOP Publishing Ltd. - 0004-637X .- 1538-4357. ; 921:1
-
Journal article (peer-reviewed)abstract
- The tight correlations between the mass of supermassive black holes (M (BH)) and their host-galaxy properties have been of great interest to the astrophysical community, but a clear understanding of their origin and fundamental drivers still eludes us. The local relations for active galaxies are interesting in their own right and form the foundation for any evolutionary study over cosmic time. We present Hubble Space Telescope optical imaging of a sample of 66 local active galactic nuclei (AGNs); for 14 objects, we also obtained Gemini near-infrared images. We use state-of-the-art methods to perform surface photometry of the AGN host galaxies, decomposing them into spheroid, disk, and bar (when present), and inferring the luminosity and stellar mass of the components. We combine this information with spatially resolved kinematics obtained at the Keck Telescopes to study the correlations between M (BH) (determined from single-epoch virial estimators) and host galaxy properties. The correlations are uniformly tight for our AGN sample, with intrinsic scatter 0.2-0.4 dex, smaller than or equal to that of quiescent galaxies. We find no difference between pseudo and classical bulges or barred and nonbarred galaxies. We show that all the tight correlations can be simultaneously satisfied by AGN hosts in the 10(7)-10(9) M (circle dot) regime, with data of sufficient quality. The M (BH)-sigma relation is also in agreement with that of AGN with M (BH) obtained from reverberation mapping, providing an indirect validation of single-epoch virial estimators of M (BH).
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| 6414. |
- Bensby, Thomas, et al.
(author)
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A Differential Study of the Oxygen Abundances in the Galactic Thin and Thick Disks
- 2004
-
In: Carnegie Observatories Astrophysics Series, Origin and Evolution of the Elements. ; 4
-
Conference paper (peer-reviewed)abstract
- First results from a study into the abundance trends of oxygen in the Galactic thin and thick disks are presented. Oxygen abundances for 63nearby F and G dwarf stars, based on very high resolution spectra (R∼215 000) and high signal-to-noise (S/N>400) of the faint forbidden oxygen line at 6300Å, have been determined. Our findings can be summarized as follows: 1) at [Fe/H]<0 the oxygen trends in thethin and thick disk are smooth and distinct, indicating their different origins, 2) [O/Fe] for the thick disk stars show a turn-over at[Fe/H]∼-0.35, indicating the peak of the enrichment from SNe type Ia to the interstellar medium, 3) the thin disk stars show a shallow decrease going from [Fe/H] ∼-0.7 to the highest metallicities with no apparent turn-over present indicating a more quiet star formation history, and 4) [O/Fe] continues to decrease at [Fe/H] > 0 without showing the leveling out that previously has been seen.
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| 6415. |
- Bensby, Thomas, et al.
(author)
-
A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
- 2011
-
In: Astrophysical Journal Letters. - 2041-8213. ; 735:2
-
Journal article (peer-reviewed)abstract
- Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes, we present detailed elemental abundances for 20 red giant stars in the outer Galactic disk, located at Galactocentric distances between 9 and 13 kpc. The outer disk sample is complemented with samples of red giants from the inner Galactic disk and the solar neighborhood, analyzed using identical methods. For Galactocentric distances beyond 10 kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically different from the solar neighborhood, and we therefore suggest that the radial scale length of the thick disk is much shorter than that of the thin disk. We make a first estimate of the thick disk scale length of L-thick = 2.0 kpc, assuming L-thin = 3.8 kpc for the thin disk. We suggest that radial migration may explain the lack of radial age, metallicity, and abundance gradients in the thick disk, possibly also explaining the link between the thick disk and the metal-poor bulge.
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| 6416. |
- Bensby, Thomas, et al.
(author)
-
A Possible Bulge - Thick Disk Connection?
- 2003
-
In: Elemental Abundances in Old Stars and Damped Lyman-alpha Systems. ; 15
-
Conference paper (peer-reviewed)abstract
- We present abundances of giant stars in the Galactic bulge and thickdisk. The stellar sample contains approximately 15 bulge giants and 20thick disk giants observed with the UVES on VLT in Chile. These resultswill be used to see if there exists an evolutionary connection betweenthe bulge and the thick disk and will also put further light into theformation of the Milky Way and the thick disk in particular.
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| 6417. |
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| 6418. |
- Bensby, Thomas, et al.
(author)
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Abundance Trends in the Inner and Outer Galactic Disk
- 2012
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In: Galactic archeology, near-field cosmology and the formation of the Milky Way (ASP Conference Series). ; 458, s. 171-174
-
Conference paper (peer-reviewed)abstract
- Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes we present detailed elemental abundances for 64 red giant stars in the inner and outer Galactic disk. For the inner disk sample (4-7 kpc from the Galactic centre) we find that stars with both thin and thick disk abundance patterns are present while for Galactocentric distances beyond 10 kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically different from the solar neighbourhood, and we therefore suggest that the radial scale length of the thick disk is much shorter than that of the thin disk. A thick disk scale-length of L-thick = 2.0 kpc, and L-thin = 3.8 kpc for the thin disk, better match the data.
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| 6419. |
- Bensby, Thomas, et al.
(author)
-
alpha-, r-, and s-process element trends in the Galactic thin and thick disks
- 2005
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 1432-0746 .- 0004-6361. ; 433, s. 185-203
-
Journal article (peer-reviewed)abstract
- From a detailed elemental abundance analysis of 102 F and G dwarf starswe present abundance trends in the Galactic thin and thick disks for 14elements (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, Ba, and Eu).Stellar parameters and elemental abundances (except for Y, Ba and Eu)for 66 of the 102 stars were presented in our previous studies (Bensbyet al. 2003, 2004a). The 36 stars that are new in this study extend andconfirm our previous results and allow us to draw further conclusionsregarding abundance trends. The s-process elements Y and Ba, and ther-element Eu have also been considered here for the whole sample for thefirst time. With this new larger sample we now have the followingresults: 1) Smooth and distinct trends that for the thin and thick disksare clearly separated; 2) The alpha-element trends for the thick diskshow typical signatures from the enrichment of SNIa; 3) The thick diskstellar sample is in the mean older than the thin disk stellar sample;4) The thick disk abundance trends are invariant with galactocentricradii (R_m); 5) The thick disk abundance trends appear to be invariantwith vertical distance (Z_max) from the Galactic plane. Adding furtherevidence from the literaure we argue that a merger/interacting scenariowith a companion galaxy to produce a kinematical heating of the stars(that make up today's thick disk) in a pre-existing old thin disk is themost likely formation scenario for the Galactic thick disk.
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| 6420. |
- Bensby, Thomas, et al.
(author)
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Chemical constraints on the formation of the Galactic thick disk
- 2012
-
In: Assembling the Puzzle of the Milky Way. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 19
-
Conference paper (peer-reviewed)abstract
- We highlight some results from our detailed abundance analysis study of 703 kinematically selected F and G dwarf stars in the solar neighbourhood. The analysis is based on spectra of high-resolution (R = 45 000 to 110 000) and high signal-to-noise (S/N approximate to 150 to 300). The main findings include: (1) at a given metallicity, the thick disk abundance trends are more alpha-enhanced than those of the thin disk; (2) the metal-rich limit of the thick disk reaches at least solar metallicities; (3) the metal-poor limit of the thin disk is around [Fe/H] approximate to -0.8; (4) the thick disk shows an age-metallicity gradient; (5) the thin disk does not show an age-metallicity gradient; (6) the most metal-rich thick disk stars at [Fe/H] approximate to 0 are significantly older than the most metal-poor thin disk stars at [Fe/H] approximate to -0.7; (7) based on our elemental abundances we find that kinematical criteria produce thin and thick disk stellar samples that are biased in the sense that stars from the low-velocity tail of the thick disk are classified as thin disk stars, and stars from the high-velocity tail of the thin disk are classified as thick disk stars; (8) age criteria appears to produce thin and thick disk stellar samples with less contamination.
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