| 1. |
- Kann, D. A., et al.
(författare)
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THE AFTERGLOWS OF SWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFT AND SWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 720:2, s. 1513-1558
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Tidskriftsartikel (refereegranskat)abstract
- We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
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| 2. |
- Lorenz, D., et al.
(författare)
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Long-period variables in NGC 147 and NGC 185
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 532
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Tidskriftsartikel (refereegranskat)abstract
- Context. Previous studies on the stellar content of the two nearby dwarf galaxies NGC 147 and NGC 185 reveal a rich population of late-type giants in both systems, including a large number of carbon-rich objects. These stars are known to show pronounced photometric variability, which can be used for a more detailed characterisation of these highly evolved stars. Owing to their well-studied parameters, these Local Group members are ideal candidates for comparative studies. Aims. Through photometric monitoring, we attempt to provide a catalogue of long-period variables (LPVs), including Mira variables, semi-regular variables, and even irregular variables in NGC 147 and NGC 185. We investigate the light variations and compare the characteristics of these two LPV populations with the results found for other galaxies, such as the LMC. Methods. We carried out time-series photometry in the i-band of the two target galaxies with the Nordic Optical Telescope (NOT), covering a time span of approximate to 2.5 years. More than 30 epochs were available for a period search. These data were then combined with single-epoch K-band photometry, also obtained with the NOT. Narrow-band photometry data from the literature was used to distinguish between O-rich and C-rich stars. Results. We report the detection of 513 LPVs in NGC 185 and 213 LPVs in NGC 147, showing amplitudes Delta i of up to approximate to 2(mag) and periods ranging between 90 and 800 days. The period-luminosity diagram for each of our target galaxies exhibits a well populated sequence of fundamental mode pulsators. The resulting period-luminosity relations we obtained are compared to relations from the literature. We discuss the universality of those relations because of which, as a side result, a correction of the distance modulus of NGC 185 may be necessary. A value of (m - M) = 24.(m)30 seems to be more appropriate to match the observed data. Only one of our two galaxies, namely NGC 185, has a significant fraction of possibly first overtone pulsators. An interpretation of this finding in terms of differences in the star-formation histories is suggested.
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| 3. |
- Lorenz, D., et al.
(författare)
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LPVs as possible distance indicators in NGC147 and NGC185
- 2012
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Ingår i: Astrophysics and Space Science Proceedings. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1570-6591 .- 1570-6605. - 9783642220173 ; , s. 169-172
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Konferensbidrag (refereegranskat)abstract
- NGC147 and NGC185 are both dwarf galaxies and companions of the M31 Galaxy. These satellites of Andromeda show similar properties in their color magnitude diagram but also striking differences concerning their stellar content of intermediate age stars as well as their amount of gas and dust. This and the fact that their small apparent separation on the sky of approximately one degree make them very interesting for comparative studies. Photometric monitoring of stars in the i-band of the two dwarf galaxies NGC147 and NGC185 covering ≈ 2.5 years resulted in the discovery of a large number of Long Period Variables (LPVs). A total of 323 LPVs in NGC 185 and 147 LPVs in NGC147 were available for further analysis. Additional single-epoch Ks-band photometry was obtained in order to compare the resulting period luminosity diagrams with those of other systems like, e.g., the Large Magellanic Cloud (LMC). Making use of narrow-band photometry a significant fraction of the detected LPVs could be identified as carbonrich. To establish a universal relation between period and luminosity for LPVs, such variables need to be studied in different galaxies. Therefore, the resulting Ks - logP relations (PLRs) were compared with those from the LMC. The PLRs of NGC147 are in good agreement with the LMC relations. In contrast, a systematic shift of the sequence of fundamental mode pulsators (labeled as C) and the sequence for first overtone pulsators (C0) suggests a revised distance estimate for NGC185.
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| 4. |
- Telting, J. H., et al.
(författare)
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FIES : The high-resolution Fiber-fed Echelle Spectrograph at the Nordic Optical Telescope
- 2014
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - : Wiley. - 0004-6337 .- 1521-3994. ; 335:1, s. 41-45
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Tidskriftsartikel (refereegranskat)abstract
- FIES is a cross-dispersed high-resolution echelle spectrograph at the 2.56 m Nordic Optical Telescope (NOT), and was optimised for throughput and stability in 2006. The major 2006 upgrade involved the relocation of FIES to a stable environment and development of a fiber bundle that offers 3 different resolution modes, and made FIES an attractive tool for the user community of the NOT. Radial-velocity stability is achieved through double-chamber active temperature control. A dedicated data reduction tool, FIEStool, was developed. As a result of these upgrades, FIES is now one of the work-horse instruments at the NOT. ((c) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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