50 research outputs found
The Stellar Composition of the Star Formation Region CMa R1. II. Spectroscopic and Photometric Observations of 9 Young Stars
We present new high and low resolution spectroscopic and photometric data of
nine members of the young association CMa R1. All the stars have circumstellar
dust at some distance as could be expected from their association with
reflection nebulosity. Four stars (HD 52721, HD 53367, LkHalpha 220 and
LkHalpha 218) show Halpha emission and we argue that they are Herbig Be stars
with discs. Our photometric and spectroscopic observations on these stars
reveal new characteristics of their variability. We present first
interpretations of the variability of HD 52721, HD 53367 and the two LkHalpha
stars in terms of a partially eclipsing binary, a magnetic activity cycle and
circumstellar dust variations, respectively. The remaining five stars show no
clear indications of Halpha emission in their spectra, although their spectral
types and ages are comparable with those of HD 52721 and HD 53367. This
indicates that the presence of a disc around a star in CMa R1 may depend on the
environment of the star. In particular we find that all Halpha emission stars
are located at or outside the arc-shaped border of the H II region, which
suggests that the stars inside the arc have lost their discs through
evaporation by UV photons from nearby O stars, or from the nearby (< 25 pc)
supernova, about 1 Myr ago.Comment: 17 pages, 13 figures, accepted by MNRA
Фотохимические реакции на поверхности полупроводников, стимулированные электронными переходами
Гранкин, В. П. Фотохимические реакции на поверхности полупроводников, стимулированные электронными переходами / В. П. Гранкин, Д. В. Тузенко // Вісник Приазовського державного технічного університету : зб. наук. праць / ПДТУ. – Маріуполь, 2001. – Вип. 11. – С. 331–338.Рассмотрены механизмы диссипации энергии и предложен стадийный механизм гетерогенных экзотермических реакций, учитывающий явление высокоэффективной электронной аккомодации. Разработан математический аппарат и система
компьютерного моделирования. Показано, что для широкозонных твердых тел с двухуровневой системой электронных ловушек электронный канал может быть
использован для управления скоростью и селективностью гетерогенной реакции
Toward Understanding the B[e] Phenomenon. II. New Galactic FS CMa Stars
FS CMa stars form a group of objects with the B[e] phenomenon that were previously known as unclassified B[e] stars or B[e] stars with warm dust (B[e]WD) until recently. They exhibit strong emission-line spectra and strong IR excesses, most likely due to recently formed circumstellar dust. These properties have been suggested to be due to ongoing or recent rapid mass exchange in binary systems with hot primaries and various types of secondaries. The first paper of this series reported an analysis of the available information about previously known Galactic objects with the B[e] phenomenon, the initial selection of the FS CMa group objects, and a qualitative explanation of their properties. This paper reports the results of our new search for more FS CMa objects in the IRAS Point Source Catalog. We present new photometric criteria for identifying FS CMa stars as well as the first results of our observations of nine new FS CMa group members. With this addition, the FS CMa group has now 40 members, becoming the largest among the dust-forming hot star groups. We also present nine objects with no evidence for the B[e] phenomenon, but with newly discovered spectral line emission and /or strong IR excesses.Fil: Miroshnichenko, A. S.. The University Of North Carolina At Greensboro; Estados UnidosFil: Manset, N.. Canada France Hawaii Telescope; Estados UnidosFil: Kusakin, A.V.. Lomonosov Moscow State University; Rusia. Fesenkov Astrophysical Institute; RusiaFil: Chentsov, E.L.. Russian Academy Of Sciences; RusiaFil: Klochkova, V. G.. Russian Academy Of Sciences; RusiaFil: Zharikov, S. V.. Universidad Nacional Autónoma de México; MéxicoFil: Gray, R. O.. Appalachian State University (appstate);Fil: Grankin, K. N.. Ulugh Beg Astronomical Institute Uzbekistan Academy Of Sciences; UzbekistánFil: Gandet, T. L.. Lizard Hollow Observatory; Estados UnidosFil: Bjorkman, K. S.. University Of Toledo (utoledo); Estados UnidosFil: Rudy, R. J.. The Aerospace Corporation; Estados UnidosFil: Lynch, D. K.. The Aerospace Corporation; Estados UnidosFil: Venturini, C. C.. The Aerospace Corporation; Estados UnidosFil: Mazuk, S.. The Aerospace Corporation; Estados UnidosFil: Puetter, R. C.. University of California at San Diego; Estados UnidosFil: Perry, R. B.. National Aeronautics and Space Administration; Estados UnidosFil: Levato, Orlando Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Grosso, Monica Gladys. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Bernabei, S.. Istituto Nazionale di Astrofisica; ItaliaFil: Polcaro, V. F.. Istituto Nazionale di Astrofisica; ItaliaFil: Viotti, R. F.. Istituto Nazionale di Astrofisica; ItaliaFil: Norci, L.. Dublin City University; IrlandaFil: Kuratov, K. S.. Fesenkov Astrophysical Institute; Kazajistá
Disk-Jet Connection in the Radio Galaxy 3C 120
We present the results of extensive multi-frequency monitoring of the radio
galaxy 3C 120 between 2002 and 2007 at X-ray, optical, and radio wave bands, as
well as imaging with the Very Long Baseline Array (VLBA). Over the 5 yr of
observation, significant dips in the X-ray light curve are followed by
ejections of bright superluminal knots in the VLBA images. Consistent with
this, the X-ray flux and 37 GHz flux are anti-correlated with X-ray leading the
radio variations. This implies that, in this radio galaxy, the radiative state
of accretion disk plus corona system, where the X-rays are produced, has a
direct effect on the events in the jet, where the radio emission originates.
The X-ray power spectral density of 3C 120 shows a break, with steeper slope at
shorter timescale and the break timescale is commensurate with the mass of the
central black hole based on observations of Seyfert galaxies and black hole
X-ray binaries. These findings provide support for the paradigm that black hole
X-ray binaries and active galactic nuclei are fundamentally similar systems,
with characteristic time and size scales linearly proportional to the mass of
the central black hole. The X-ray and optical variations are strongly
correlated in 3C 120, which implies that the optical emission in this object
arises from the same general region as the X-rays, i.e., in the accretion
disk-corona system. We numerically model multi-wavelength light curves of 3C
120 from such a system with the optical-UV emission produced in the disk and
the X-rays generated by scattering of thermal photons by hot electrons in the
corona. From the comparison of the temporal properties of the model light
curves to that of the observed variability, we constrain the physical size of
the corona and the distances of the emitting regions from the central BH.Comment: Accepted for publication in the Astrophysical Journal. 28 pages, 21
figures, 2 table
A new spectroscopic and interferometric study of the young stellar object V645 Cyg
We present the results of high-resolution optical spectroscopy,
low-resolution near-IR spectroscopy and near-infrared speckle interferometry of
the massive young stellar object candidate V645 Cyg, acquired to refine its
fundamental parameters and the properties of its circumstellar envelope.
Speckle interferometry in the - and -bands and an optical spectrum in the
range 5200--6680 \AA with a spectral resolving power of = 60 000 were
obtained at the 6-m telescope of the Russian Academy of Sciences. Another
optical spectrum in the range 4300--10500 \AA with = 79 000 was obtained at
the 3.6-m CFHT. Low-resolution spectra in the ranges 0.46--1.4 m and
1.4--2.5 m with 800 and 700, respectively, were obtained
at the 3-m Shane telescope of the Lick Observatory. Using a novel kinematical
method based on the non-linear modeling of the neutral hydrogen density profile
in the direction toward the object, we propose a distance of 0.2
kpc. We also suggest a revised estimate of the star's effective temperature,
T25 000 K. We resolved the object in both - and -bands.
We conclude that V645 Cyg is a young, massive, main-sequence star, which
recently emerged from its cocoon and has already experienced its protostellar
accretion stage. The presence of accretion is not necessary to account for the
high observed luminosity of (2--6) M yr. The
receding part of a strong, mostly uniform outflow with a terminal velocity of
800 km s is only blocked from view far from the star, where
forbidden lines form.Comment: 14 pages, 10 figure
X-ray Study of the Intermediate-Mass Young Stars Herbig Ae/Be Stars
We present the ASCA results of intermediate-mass pre-main-sequence stars
(PMSs), or Herbig Ae/Be stars (HAeBes). Among the 35 ASCA pointed-sources, we
detect 11 plausible X-ray counterparts. X-ray luminosities of the detected
sources in the 0.5-10 keV band are in the range of log LX ~30-32 ergs s-1,
which is systematically higher than those of low-mass PMSs. This fact suggests
that the contribution of a possible low-mass companion is not large. Most of
the bright sources show significant time variation, particularly, two HAeBes -
MWC 297 and TY CrA - exhibit flare-like events with long decay timescales
(e-folding time ~ 10-60 ksec). These flare shapes are similar to those of
low-mass PMSs. The X-ray spectra are successfully reproduced by an absorbed one
or two-temperature thin-thermal plasma model. The temperatures are in the range
of kT ~1-5 keV, which are significantly higher than those of main-sequence OB
stars (kT < 1 keV). These X-ray properties are not explained by wind driven
shocks, but are more likely due to magnetic activity. On the other hand, the
plasma temperature rises as absorption column density increases, or as HAeBes
ascend to earlier phases. The X-ray luminosity reduces after stellar age of a
few x10^6 years. X-ray activity may be related to stellar evolution. The age of
the activity decay is apparently near the termination of jet or outflow
activity. We thus hypothesize that magnetic activity originates from the
interaction of the large scale magnetic fields coupled to the circumstellar
disk. We also discuss differences in X-ray properties between HAeBes and
main-sequence OB stars.Comment: 51 pages, 17 figures, accepted by Ap