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| 2. |
- Eriksson, Mattias, et al.
(författare)
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Fluorescence Fe II lines as traces of fast outflows of white dwarf winds
- 2007
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Ingår i: Baltic Astronomy. - 1392-0049. ; 16:01, s. 95-97
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Tidskriftsartikel (refereegranskat)abstract
- A set of equations are put into a code forming a procedure to derive intensities of fluorescence lilies based on both physical properties of the fluorescent plasma and its location relative to the origin of the pumping emission. In a first test, the code is applied to symbiotic stars, and effort is made to explain the circumstances under which the two known Fell channels pumped by C IV are activated. For the channel at 1548.204 angstrom, which is most frequently observed to be active, there is a good agreement between the results of the calculations and the observed Fell line strengths. Fluorescence lines resulting from pumping through the other channel at 1548.411 angstrom can occur, according to the results of the calculations, only in the systems where a fast outflow from the white dwarf wind is present. The evidences of the white dwarf winds are found in the literature for all the symbiotic systems in which observation of the Fell fluorescence lines from the w(2)D(3/2) level is reported.
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| 3. |
- Foley, S., et al.
(författare)
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Global Characteristics Of Gamma-Ray Bursts Observed With Integral
- 2009
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Ingår i: Baltic Astronomy. - 1392-0049. ; 18:3-4, s. 279-283
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Tidskriftsartikel (refereegranskat)abstract
- The gamma-ray instruments on board INTEGRAL have detected and localized 62 gamma-ray bursts (GRBs) to date. The peak flux distribution of these bursts shows that INTEGRAL detects proportionally more weak GRBs than Swift because of its higher sensitivity in a smaller field of view. Spectral lags, i.e., the time delay in the arrival of low-energy gamma rays with respect to high-energy gamma rays, are measured for 31 of the GRBs. Two groups are identified in the spectral lag distribution of INTEGRAL GRBs, one with short lags < 0.75 s (between 25-50 keV and 50-300 keV) and one with long lags > 0.75 s. Most of the long-lag GRBs are inferred to have low redshifts because of their long spectral lags. They are mainly observed in the direction of the supergalactic plane and hence reflect the local large-scale structure of the Universe. This low-luminosity population appears to be distinct from typical cosmological GRBs.
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| 4. |
- Kucinskas, A., et al.
(författare)
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Magnitude And Color Transformations Between Sirius And 2Mass Photometric Systems
- 2008
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Ingår i: Baltic Astronomy. - 1392-0049. ; 17:3-4, s. 283-292
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Tidskriftsartikel (refereegranskat)abstract
- We provide magnitude and color transformations between two near-infrared photometric systems, 2MASS and SIRIUS, the latter currently implemented with the three-Channel SIRIUS camera on 1.4 m Infrared Survey Facility telescope at the South African Astronomical Observatory. The transformation equations are derived using a carefully selected sample of 32 770 stars in the. Large and Small Magellanic Clouds that have high quality observations available in both photometric systems. The derived transformations are valid in the color range -0.1 < (J - H)(SIRIUS) < 1.15, -0.05 < (H - K-s)(SIRIUS) < 0.7 and -0.1 < (J - K-s)(SIRIUS) < 1.7.
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| 5. |
- Kucinskas, Arunas, et al.
(författare)
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Star Formation Histories with Gaia: the Galaxy and Beyond
- 2003
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Ingår i: Baltic Astronomy. - 1392-0049. ; 12:4, s. 526-531
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Tidskriftsartikel (refereegranskat)abstract
- ESA's Gaia mission will provide accurate astrometric, photometric andspectroscopic data for millions of stars in the Galaxy and beyond. Wediscuss the prospects of using this vast amount of astrophysicalinformation for understanding star formation histories in the Galaxy andits immediate neighbors within the Local Group.
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| 6. |
- Stempels, Henricus C.
(författare)
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Anders Celsius' contributions to meridian arc measurements and the establishment of an astronomical observatory in Uppsala
- 2011
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Ingår i: Baltic Astronomy. - 1392-0049. ; 20:2, s. 179-185
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Tidskriftsartikel (refereegranskat)abstract
- Astronomy has been on the curriculum of Uppsala University from at least the middle of the 15th century. However, since Uppsala also was the ecclesiastical centre of Sweden, the acceptance of new ideas, such as the Copernican heliocentric system, was slow. At the same time, more peripheral universities in the Swedish empire, including Dorpat/Tartu, enjoyed a larger freedom. It was not until the early 18th century that a 'modern' astronomy emerged in Uppsala. This effort was to a large extent led by Anders Celsius (1701-1744), who was able to establish good international contacts with astronomers in continental Europe. Celsius participated in De Maupertuis' expedition to the far north of Sweden, in order to measure the meridian arc and determine the shape of the Earth. This paper explores how Celsius became involved in De Maupertuis' expedition, and how this effort paved the way to the establishment of a fully equipped astronomical observatory, including an extensive collection of books and instruments, most of which survives up to this day.
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| 7. |
- Tautvaisiene, Grazina, et al.
(författare)
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Selecting a photometric system for GAIA: C, N, O and alpha-process elements
- 2003
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Ingår i: Baltic Astronomy. - 1392-0049. ; 12:4, s. 532-538
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Tidskriftsartikel (refereegranskat)abstract
- The sensitivity of stellar spectra to C, N, O and alpha-process element abundances is discussed with the aim to be taken into account when selecting a photometric system for the GAIA orbiting observatory. On the basis of a spectrometric, photometric and theoretical study of spectra of evolved first-ascent giants and clump stars in the open cluster NGC 7789 it is demonstrated that evolutionary alterations of carbon and nitrogen abundances can cause noticeable spectral changes and, if not taken into account, may yield misleading photometric [Fe/H] determinations. Carbon features in stellar atmospheres show a particularly complex behavior being dependent on mixing processes in stars, on the stellar surface gravity and on the abundance of oxygen which can also be altered by different reasons. NH bands could serve for the evaluation of mixing processes in stars and the interpretation of carbon dominated spectral regions. Abundances of alpha-process elements can be evaluated photometrically by using the direct indicators -- Ca II H and K lines and Mg I b triplet.
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