The photometric evolution of FU Orionis objects: disc instability and wind–envelope interaction     

C. Clarke  G. Lodato  S. Y. Melnikov  M. A. Ibrahimov 《Monthly notices of the Royal Astronomical Society》2005,361(3):942-954

We present the results of a photometric monitoring campaign of three well-studied FU Orionis systems (FU Orionis, V1057 Cygni and V1515 Cygni) undertaken at Maidanak Observatory between 1981 and 2003. When combined with photometric data in the literature, this data base provides a valuable resource for searching for short time-scale variability – both periodic and aperiodic – as well as for studying the secular evolution of these systems. In the case of V1057 Cyg (which is the system exhibiting the largest changes in brightness since it went into outburst) we compare the photometric data with time-dependent models. We show that prior to the end of the 'plateau' stage in 1996, the evolution of V1057 Cyg in the V –( B − V ) colour–magnitude diagram is well represented by disc instability models in which the outburst is triggered by some agent – such as an orbiting planet – in the inner disc. Following the end of the plateau phase in 1996, the dimming and irregular variations are consistent with occultation of the source by a variable dust screen, which has previously been interpreted in terms of dust condensation events in the observed disc wind. Here we instead suggest that this effect results from the interaction between the wind and an infalling dusty envelope, the existence of this envelope having been previously invoked in order to explain the mid-infrared emission of FU Orionis systems. We discuss how this model may explain some of the photometric and spectroscopic characteristics of FU Orionis systems in general.  相似文献   

Evidence for energy injection and a fine-tuned central engine at optical wavelengths in GRB 070419A     

A. Melandri  C. Guidorzi  S. Kobayashi  D. Bersier  C. G. Mundell  P. Milne  A. Pozanenko  W. Li  A. V. Filippenko  Y. Urata  M. Ibrahimov  I. A. Steele  A. Gomboc  R. J. Smith  N. R. Tanvir  E. Rol  K. Huang 《Monthly notices of the Royal Astronomical Society》2009,395(4):1941-1949

We present a comprehensive multiwavelength temporal and spectral analysis of the 'fast rise exponential decay' GRB 070419A. The early-time emission in the γ-ray and X-ray bands can be explained by a central engine active for at least 250 s, while at late times the X-ray light curve displays a simple power-law decay. In contrast, the observed behaviour in the optical band is complex (from 10² up to 10⁶ s). We investigate the light-curve behaviour in the context of the standard forward/reverse shock model; associating the peak in the optical light curve at ∼450 s with the fireball deceleration time results in a Lorenz factor  Γ≈ 350  at this time. In contrast, the shallow optical decay between 450 and 1500 s remains problematic, requiring a reverse shock component whose typical frequency is above the optical band at the optical peak time for it to be explained within the standard model. This predicts an increasing flux density for the forward shock component until   t ∼ 4 × 10⁶ s  , inconsistent with the observed decay of the optical emission from   t ∼ 10⁴ s  . A highly magnetized fireball is also ruled out due to unrealistic microphysic parameters and predicted light-curve behaviour that is not observed. We conclude that a long-lived central engine with a finely tuned energy injection rate and a sudden cessation of the injection is required to create the observed light curves, consistent with the same conditions that are invoked to explain the plateau phase of canonical X-ray light curves of γ-ray bursts.  相似文献   

First Telescope of the Russian–Cuban Observatory     

Bisikalo  D. V.  Sachkov  M. E.  Ibrahimov  M. A.  Savanov  I. S.  Nalivkin  M. A.  Naroenkov  S. A.  Fateeva  A. M.  Shugarov  A. S.  Mata  Rudy Montero  Pons  Omar Rodriguez  Rodriguez Uratsuka  Marta R. 《Astronomy Reports》2022,66(1):38-41

Astronomy Reports - Beginning of operation of the first Russian–Cuban Observatory telescope, a wide-field 20-cm robotic telescope installed at the observational site optical station in...  相似文献   

Multiband photometric detection of a huge flare on the M9 dwarf 2MASSW J1707183+643933     

Boris Rockenfeller  Coryn A. L. Bailer-Jones  Reinhard Mundt  Mansur A. Ibrahimov 《Monthly notices of the Royal Astronomical Society》2006,367(1):407-411

We present simultaneous UV , G , R and I monitoring of 19 M dwarfs that reveal a huge flare on the M9 dwarf with an amplitude in the UV of at least 6 mag. This is one of the strongest detections ever of an optical flare in an M star and one of the first in an ultracool dwarf (spectral types later than about M7). Four intermediate-strength flares  (Δ m _UV < 4 mag)  were found in this and three other targets. For the whole sample we deduce a flare probability of 0.013 (rate of  0.022 h⁻¹  ), and  0.049 (0.090 h⁻¹)  for 2M1707+64 alone. Deviations of the flare emission from a blackbody is consistent with strong  Hα  line emission. We also confirm our previously found rotation period for 2M1707+64 and determine it more precisely to be  3.619 ± 0.015 h  .  相似文献   

Opposition effect of Trojan asteroids     

V.G. Shevchenko  I.N. Belskaya  I.G. Slyusarev  Yu.N. Krugly  V.G. Chiorny  N.M. Gaftonyuk  Z. Donchev  V. Ivanova  M.A. Ibrahimov  Sh.A. Ehgamberdiev  I.E. Molotov 《Icarus》2012,217(1):202-208

CCD-photometry of three Jupiter Trojan asteroids were carried out to study their opposition effect. We obtained well-sampled magnitude–phase curves for (588) Achilles, (884) Priamus, and (1143) Odysseus in the maximal attainable phase angle range down to 0.1–0.2°. The magnitude–phase relations have a linear behavior in all observed range of phase angles and do not show any non-linear opposition brightening. We have not found any confident differences between phase slopes measured in B, V and R bands. The values of the measured phase slopes of Trojans are different from available data for Centaurs. They are within the range of phase slopes measured for some low-albedo main belt asteroids, also exhibit a linear behavior down to small phase angles. An absence of non-linear opposition brightening puts constraints on the surface properties of the studied objects, assuming very dark surfaces where single scattering plays dominating role.We also determined the rotation periods, amplitudes, the values of color indexes B–V and V–R, and the absolute magnitudes of these asteroids.  相似文献   

The stellar composition of the star formation region CMa R1 – I. Results from new photometric and spectroscopic classifications     

V. S. Shevchenko  O. V. Ezhkova  M. A. Ibrahimov  M. E. van den Ancker  H. R. E. Tjin A Djie 《Monthly notices of the Royal Astronomical Society》1999,310(1):210-222

A new photometric and spectroscopic survey of the star formation region (SFR) CMa R1 is described. In a sample of 165 stars brighter than 13th mag, 88 stars were found to be probable members of the SFR. They are defined as early-type stars with E ( B − V )0.16 mag, which corresponds to a distance of about 1 kpc. 74 of the probable members are B stars. 19 stars are possibly associated with an IRAS point source. We derive a most probable distance of 1050±150 pc to the association. It appears that about 80 candidate members are pre-main-sequence stars with ages lower than 6 million years, while the main sequence extends over 6.0–7.6 mag, which is consistent with star formation starting about 8 million years ago and continuing until at least half a million years ago. Two bright B stars in the association (GU CMa and FZ CMa) seem to be much older and probably do not originate from the same star formation episode. The star formation efficiency appears to increase roughly monotonically with time up to half a million years ago. From our data, we conclude that only a minor fraction of the stars has been created through the scenario suggested by Herbst & Assousa, in which the members of CMa R1 form by compression of ambient material by a supernova shock wave. An extensive search for candidate members with H α emission did not reveal new Herbig Ae/Be candidates, so that the number of stars in this class seems to be limited to four: Z CMa, LkH α 218, LkH α 220 and possibly HD 53367.  相似文献   

Seeing and atmospheric extinction at Mt. Maidanak observatory from observations with the 1.5-m AZT-22 telescope     

B. P. Artamonov  V. V. Bruevich  A. S. Gusev  O. V. Ezhkova  M. A. Ibrahimov  S. P. Ilyasov  S. A. Potanin  Yu. A. Tillaev  Sh. A. Ehgamberdiev 《Astronomy Reports》2010,54(11):1019-1031

We have determined the realistic seeing of the 1.5-m AZT-22 telescope of the Mt. Maidanak Observatory (Astronomical Institute, Uzbek Academy of Sciences) using more than 20 000 CCD frames with stellar images in the UBV RI bands acquired in 1996–2005: ε = 1.065″ in the V band. The characteristic seeing reduced to unit air mass, ε _med ^V (M(z) = 1), is 0.945″. We derived color equations for the CCD detectors used with the telescope. Atmospheric-extinction coefficients in different photometric bands were also determined. The mean V -band atmospheric extinction is 0.20 ^m ± 0.04 ^m . The time needed for the conditions to settle, in the free atmosphere as well as inside the telescope dome, is 2–2.5 hours after the end of astronomical twilight. For nights with ε _med ^V > 0.9″, we find a persistent difference between the seeing found at this telescope and measured simultaneously with a differential image motion monitor, amounting to ∼0.1 ^m .  相似文献