| 1. |
- Boyarchuk, A. A., et al.
(författare)
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Scientific problems addressed by the Spektr-UV space project (world space Observatory-Ultraviolet)
- 2016
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Ingår i: Astronomy reports (Print). - 1063-7729 .- 1562-6881. ; 60:1, s. 1-42
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Tidskriftsartikel (refereegranskat)abstract
- The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory-Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115-310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems.
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| 2. |
- Johansson, Sveneric, et al.
(författare)
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The Possibility of Resonance-Enhanced Two-Photon Ionization of Ne and Ar Atoms in Astrophysical Plasmas
- 2004
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Ingår i: Astronomy Reports. - : Pleiades Publishing Ltd. - 1063-7729 .- 1562-6881. ; 48:5, s. 399-406
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Tidskriftsartikel (refereegranskat)abstract
- We consider possible schemes for the resonance-enhanced two-photon ionization (RETPI) of Ne and Ar atoms under the action of bichromatic radiation of intense resonance lines of HI, HeI, and HeII in a radiation-rich astrophysical plasma. The ionization rate is comparable to or exceeds the recombination rate in rarified astrophysical plasma, which leads to the accumulation of singly ionized ions with a subsequent transition to the higher ionization state via RETPI. We consider the RETPI reaction chains NeI ...
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| 3. |
- Kalenskii, S. V., et al.
(författare)
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Class I methanol masers in low-mass star-forming regions
- 2013
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Ingår i: Astronomy Reports. - : Pleiades Publishing Ltd. - 1562-6881 .- 1063-7729. ; 57:2, s. 120-127
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Tidskriftsartikel (refereegranskat)abstract
- Results of observations of Class I methanol masers in regions of low-mass star formation (MMIL) are summarized and analyzed. Four masers were detected at 44, 84, and 95 GHz towards "chemically active" bipolar outflows in the low-mass star-forming regions NGC1333 I4A, NGC 1333 I2A, HH 25, and L1157. Another maser was found at 36 GHz towards a similar outflow in NGC 2023. Thus, all the detected MMILs are associated with chemically active outflows. The brightness temperatures of the strongest 44-GHz maser spots in NGC 1333 I4A, HH 25, and L1157 exceed 2000 K, whereas the brightness temperature in NGC 1333 I2A is only 176 K, although a rotational-diagram analysis shows that this last source is also amaser. The flux densities of the newly detectedmasers are no higher than 18 Jy, and are much lower than those of strong masers in regions of high-mass star formation (MMIH). The MMIL luminosities match the maser luminosity-protostar luminosity relation established earlier for MMIHs. No MMIL variability was detected in 2004-2011. The radial velocities of the newly detected masers are close to the systemic velocities of the associated regions, except for NGC 2023, where the maser radial velocity is lower than the systemic velocity by approximately 3.5 km/s. Thus, the main MMILproperties are similar to those of MMIHs. MMILs are likely to be an extension of the MMIH population toward lower luminosities of both the masers and the associated young stellar objects. The results of VLA observations of MMILs can be explained using a turbulent-cloud model, which predicts that compact maser spots can arise in extended sources because the coherence lengths along some directions randomly appear to be longer than the mean coherence length in a turbulent velocity field. However, one must assume that the column density of methanol towardM1, the strongest maser in L1157, is appreciably higher than the mean column density of the clump B0a where the maser arises. The shape of the maser lines in L1157, forming double profiles with a red asymmetry, may indicate that the masers arise in collapsing clumps. However, although this model may be correct for L1157, it is specific to this source, since none of the other masers observed exhibited a double profile.
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| 4. |
- Kalenskii, S. V., et al.
(författare)
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Spectral scan of the star-forming region DR21(OH). Observations and LTE analysis
- 2010
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Ingår i: Astronomy Reports. - 1562-6881 .- 1063-7729. ; 54:4, s. 295-316
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Tidskriftsartikel (refereegranskat)abstract
- Seventy-eight molecules have been detected as a result of a spectral survey of the star-forming region DR21(OH) at 84-115 GHz. The abundances of most molecules are typical of those in the dense cores of molecular clouds. The rotational temperatures derived using the lines of most molecules fall in the range 9-56 K, which is also typical for dense cores. However, emission from high-lying levels of methanol and sulfur dioxide was detected; since the rotational temperatures for methanol and sulfur dioxide are 252 and 186 K, this indicates the presence of hot regions. Another fact indicating the existence of hot regions is the detection of CH3OCHO, CH3CH2OH, and CH3OCH3, which have thus far been observed only in hot cores and shock-heated regions. An interesting result is the tentative detection of the J = 2 - 1, v = 1 SiO line, with the upper level energy of 1775 K. This is probably a maser line, similar to but weaker than the well-known SiO masers in the star-forming regions Orion-KL,W51(N), and Sgr B2(N).
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| 5. |
- Kalenskii, S. V., et al.
(författare)
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Spectral survey of the star-forming region W51 e1/e2 at 3 mm
- 2010
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Ingår i: Astronomy Reports. - : Pleiades Publishing Ltd. - 1562-6881 .- 1063-7729. ; 54:12, s. 1084-1104
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Tidskriftsartikel (refereegranskat)abstract
- A spectral survey of the W51 e1/e2 star-forming region at 84-115 GHz has yielded detections of 105 molecules and their isotopic species, from simple diatomic or triatomic molecules, such as CO, CS, HCN, up to complex organic compounds, such as CH3OCH3, CH3COCH3, and C2H5OOCH. Ninety-three lines that are absent from the Lovas list of molecular lines observed from space were detected, and approximately half of these were identified. A significant number of the detectedmolecules are typical for hot cores. These include the neutral molecules CH3OCHO, C2H5OH, CH3COCH3 etc., which are currently believed to exist in the gas phase only in hot cores and shock-heated gas. In addition, vibrationally excited SiO, C4H, HCN, l-C3H, HCCCN, CH3CN, CH3OH, H2O, and SO2 lines with upper-level temperatures of several hundred Kelvin were found. Such lines can arise only in hot gas with temperatures of the order of 100 K or higher. Apart from neutral molecules, various molecular ions were also detected. Some of these (N2H+, HCO+, HCS+) usually exist in molecular clouds with high visual extinctions A (V) . At the same time, the CF+ ion should be observed in photon-dominated regions with A (V) values of about unity or lower. An interesting result is the tentative detection of two molecules that have thus far been observed only in the atmospheres of late-type giant stars-MgCN and NaCN. This suggests that the conditions in the hottest W51 regions (probably, in the vicinities of protostars) are close to those in the atmospheres of giant stars. It would be desirable to search for other lines of these molecules to verify these tentative detections. Analysis of the radial velocities of the detected molecules suggests that the contribution from the e2 core dominates the emission of some O-bearing molecules (CH3OCHO, CH3CH2OH), while the contribution of the e1 core dominates the emission of some N-bearing molecules (e.g., CH3CH2CN). Thus, the molecular composition of the e2 core may be closer to the composition of the "Compact Ridge" in OMC-1, while the composition of the e1 core is closer to that for the "Hot Core" in the same cloud.
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| 6. |
- Kalenskii, S. V., et al.
(författare)
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VLA Observations of Class I Methanol Masers in the Region of Low-Mass Star Formation L1157
- 2010
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Ingår i: Astronomy Reports. - 1562-6881 .- 1063-7729. ; 54:10, s. 932-939
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of VLA observations of a maser candidate in the low-mass star formation region L1157 in the 7(0)-6(1) A(+) transition at 44 GHz. The line is emitted by a compact, undoubtedly maser source associated with clump B0a, which is seen in maps of L1157 in thermal lines of methanol and other molecules. A much weaker compact source is associated with clump B1a, which is brighter than B0a in thermal methanol lines. The newly detected masers may form in thin layers of turbulent post-shock gas. In this case, the maser emission may be beamed, so that only an observer located in or near the planes of the layers can observe strong masers. On the other hand, the maser lines are double with a "red" asymmetry, indicating that the masers may form in collapsing clumps. A detailed analysis of collapsing-cloud maser models and their applicability to the masers in L1157 will be developed in subsequent papers.
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| 7. |
- Kirsanova, M. S., et al.
(författare)
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Gas kinematics in high-mass star-forming regions from the Perseus spiral arm
- 2017
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Ingår i: Astronomy Reports. - 1562-6881 .- 1063-7729. ; 61:9, s. 760-774
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Tidskriftsartikel (refereegranskat)abstract
- We present results of a survey of 14 star-forming regions from the Perseus spiral armin CS (2-1) and (CO)-C-13 (1-0) lines with the Onsala Space Observatory 20 m telescope. Maps of 10 sources in both lines are obtained. For the remaining sources a map in just one line or a single-point spectrum is obtained. On the basis of newly obtained and published observational data we consider the relation between velocities of the "quasi-thermal" CS (2-1) line and 6.7 GHz methanol maser line in 24 high-mass star-forming regions in the Perseus arm. We show that, surprisingly, velocity ranges of 6.7 GHz methanol maser emission are predominantly red-shifted with respect to corresponding CS (2-1) line velocity ranges in the Perseus arm. We suggest that the predominance of the "red-shifted masers" in the Perseus arm could be related to the alignment of gas flows caused by the large-scalemotions in the Galaxy. Large-scale galactic shock related to the spiral structure is supposed to affect the local kinematics of the star-forming regions. Part of the Perseus arm, between galactic longitudes from 85A degrees to 124A degrees , does not contain blue-shifted masers at all. Radial velocities of the sources are the greatest in this particular part of the arm, so the velocity difference is clearly pronounced. (CO)-C-13 (1-0) and CS (2-1) velocity maps of G183.35-0.58 show gas velocity difference between the center and the periphery of the molecular clump up to 1.2 km s(-1). Similar situation is likely to occur in G85.40-0.00. This can correspond to the case when the large-scale shock wave entrains the outer parts of a molecular clump in motion while the dense central clump is less affected by the shock.
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| 8. |
- Pakhomov, Yu, V, et al.
(författare)
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Hyperfine Splitting in the VALD Database of Spectral-line Parameters
- 2019
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Ingår i: Astronomy reports (Print). - : PLEIADES PUBLISHING INC. - 1063-7729 .- 1562-6881. ; 63:12, s. 1010-1021
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Tidskriftsartikel (refereegranskat)abstract
- The Vienna Atomic Line Database (VALD) has been supplemented with new data and new functionality-the possibility of taking into account the effect of hyperfine splitting (HFS) of atomic levels in the analysis of line profiles. This has been done through the creation of an ancillary SQL database with the HFS constants for atomic levels of 58 isotopes of 30 neutral and singly-ionized atoms. The completeness of the collected data and new opportunities for studies of stars of various spectral types is analyzed. The database enables analysis of splitting of up to 60% of lines with measurable effects in the ultraviolet (lambda >= 1000 angstrom), and up to 100% of such lines in the optical and infrared ranges (lambda >= 25 000 angstrom) for A-M stars. In the spectra of hot O-B stars, it is necessary to use laboratory measurements for atoms in the second and higher stages of ionization.
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| 9. |
- Petrushevska, T., et al.
(författare)
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Prospects for Strongly Lensed Supernovae Behind Hubble Frontier Fields Galaxy Clusters with the James Webb Space Telescope
- 2018
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Ingår i: Astronomy reports (Print). - 1063-7729 .- 1562-6881. ; 62:12, s. 917-925
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Tidskriftsartikel (refereegranskat)abstract
- Measuring time delays from strongly lensed supernovae (SNe) is emerging as a novel and independent tool for estimating the Hubble constant (H-0). This is very important given the recent discord in the value of H-0) from two methods that probe different distance ranges. The success of this technique will rely of our ability to discover strongly lensed SNe with measurable time delays. Here, we present the magnifications and the time delays for the multiply-imaged galaxies behind the Hubble Frontier Fields (HFF) galaxy clusters, by using recently published lensing models. Continuing on our previous work done for Abell 1689 (A1689) and Abell 370, we also show the prospects of observing strongly lensed SNe behind the HFF clusters with the upcoming James Webb Space Telescope (JWST). With four 1-hour visits in one year, the summed expectations of all six HFF clusters are similar to 0.5 core-collapse (CC) SNe and 0.06 Type Ia SNe (SNe Ia) in F115W band, while with F150W the expectations are higher, similar to 0.9 CC SNe and similar to 0.06 SNe Ia. These estimates match those expected by only surveying A1689, proving that the performance of A1689 as gravitational telescope is superior. In the five HFF clusters presented here, we find that F150W will be able to detect SNe Ia (SNe IIP) exploding in 93 (80) pairsmultiply-imaged galaxies with time delays of less than 5 years.
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| 10. |
- Pirogov, L. E., et al.
(författare)
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Multifrequency Studies of Massive Cores with Complex Spatial and Kinematic Structures
- 2016
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Ingår i: Astronomy Reports. - : Pleiades Publishing Ltd. - 1562-6881 .- 1063-7729. ; 60:10, s. 904-923
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Tidskriftsartikel (refereegranskat)abstract
- Five regions of massive-star formation have been observed in various molecular lines in the frequency range similar to 85-89 GHz. The studied regions comprise dense cores, which host young stellar objects. The physical parameters of the cores are estimated, including the kinetic temperatures (similar to 20-40 K), the sizes of the emitting regions (similar to 0.1-0.6 pc), and the virial masses (similar to 40-500 M-circle dot). The column densities and abundances of various molecules are calculated assuming Local Thermodynamical Equilibrium(LTE). The core in 99.982+4.17, which is associated with the weakest IRAS source, is characterized by reduced molecular abundances. The molecular line widths decrease with increasing distance from the core centers (b). For b greater than or similar to 0.1 pc, the dependences Delta V (b) are close to power laws (alpha b(-p)), where p varies from similar to 0.2 to similar to 0.5, depending on the object. In four cores, the asymmetries of the optically thick HCN(1-0) and HCO+(1-0) lines indicates systematic motions along the line of sight: collapse in two cores and expansion in two others. Approximate estimates of the accretion rates in the collapsing cores indicate that the forming stars have masses exceeding the solar mass.
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