Star cluster formation and disruption time-scales – II. Evolution of the star cluster system in the fossil starburst of M82     

Richard de Grijs  Nate Bastian  Henny J. G. L. M. Lamers 《Monthly notices of the Royal Astronomical Society》2003,340(1):197-209

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Another new small-amplitude red variable star with period of about one day in the globular cluster M4     

Yao Bao-an  Sheng Chang-jun  Zhang Chun-sheng  Hu Han-ming  Lin Qing 《Chinese Astronomy and Astrophysics》2006,30(4):351-354

A66 is a red star located at the lowest end of the red giant branch (near the top of the sub-giant branch) of the globular cluster M4. According to its location on the GM diagram, A66 may be a cluster member. No proper motion and radial velocity determinations are available up to date.

We discovered that A66 is a small-amplitude new variable star with a period of about one day and the peak to peak amplitude is about 0.05 mag in V.

However, if its membership can be confirmed by proper motion and radial velocity determinations, the cause of light variation may be not pulsation. This is because according to Xiong's theory, a red star at such low luminosity can not pulsate at a period longer than 0.1 day. Then other causes such as EW type eclipsing variable star or rotation of a spotted star might be responsible. Otherwise A66 is not a cluster member.  相似文献   

Doppler Imaging of Rapidly-Rotating M Stars     

Klaus G. Strassmeier 《Astrophysics and Space Science》2006,304(1-4):333-336

With the advent of 8–12m-class telescopes and powerful new spectrographs, we can now extend the Doppler-imaging technique to the cool (and faint) end of the main sequence. At a spectral type of approximately M2, stars are thought to become fully convective and cannot possess an overshoot layer between a radiative core and a convective envelope which, as in the case of the Sun and similar stars, likely harbors the dynamo. Therefore, one could expect a fundamentally different magnetic-field topology than on the Sun and thus a qualitatively different surface temperature distribution with new, hitherto unknown, magnetic activity phenomena. Unfortunately, most single M stars do not rotate sufficiently fast for Doppler imaging and one has to “use” binaries or pre-main-sequence stars in which M stars appear spun up or, in binaries, synchronized to the orbital motion.  相似文献   

Variable stars in the core of the globular cluster M3     

Jay Strader  Henry O. Everitt  Stephen Danford 《Monthly notices of the Royal Astronomical Society》2002,335(3):621-627

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Inverse radiation modeling of Titan's atmosphere to assimilate solar aureole imager data of the Huygens probe     

B. Grieger  M.T. Lemmon 《Planetary and Space Science》2003,51(2):147-158

During the descent of the Huygens probe through Titan's atmosphere in January 2005, the Descent Imager/Spectral Radiometer (DISR) will perform upward and downward looking measurements at various spectral ranges and spatial resolutions. This internal radiation density could be estimated by radiative transfer calculations for Titan's atmosphere. However, to do this, the optical properties—i.e. volume extinction coefficient, single scattering albedo and scattering phase function—have to be prescribed at every altitude, and these are apriori not known. Herein, an inverse approach is investigated, which retrieves the single scattering albedo and the phase function of the aerosols from DISR observations. The method uses data from a DISR subinstrument, the Solar Aureole imager (SA), to estimate the optical properties of the atmospheric layer between two successive observation altitudes. A unique solution for one layer can in principle be calculated directly from a linear system of equations, but due to the sparseness of the data and the unavoidable noise in the measurements, the inverse problem is ill-posed. The problem is stabilized by the regularization method requiring smoothness of the resultant solution. A consistent set of solutions for all layers is obtained by iterating several times downward and upward through the layers. The method is tested in a simulated radiation density scenario for Titan, which is based on a microphysical aerosol model for the haze layer. Within this scenario, the expected coverage of SA data allows a reconstruction of the angular dependence of the scattering phase function with an explained variance better than 90%.  相似文献   

High-velocity regions in planetary nebulae     

Krzysztof Gesicki  Albert A. Zijlstra 《Monthly notices of the Royal Astronomical Society》2003,338(2):347-359

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Star cluster formation and disruption time-scales – I. An empirical determination of the disruption time of star clusters in four galaxies     

S. G. Boutloukos †  H. J. G. L. M. Lamers 《Monthly notices of the Royal Astronomical Society》2003,338(3):717-732

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Gas-phase models for the evolved planetary nebulae NGC 6781, M4-9 and NGC 7293     

A. Ali  O.M. Shalabiea  M.S. El-Nawawy  T.J. Millar 《Monthly notices of the Royal Astronomical Society》2001,325(2):881-885

We have studied the chemistry of the molecular gas in evolved planetary nebulae. Three pseudo-time-dependent gas-phase models have been constructed for dense (10⁴–10⁵ cm⁻³) and cool ( T ∼15 K) clumpy envelopes of the evolved nebulae NGC 6781, M4-9 and NGC 7293. The three nebulae are modelled as carbon-rich stars evolved from the asymptotic giant branch to the late planetary nebula phase. The clumpy neutral envelopes are subjected to ultraviolet radiation from the central star and X-rays that enhance the rate of ionization in the clumps. With the ionization rate enhanced by four orders of magnitude over that of the ISM, we find that resultant abundances of the species HCN, HNC, HC₃N and SiC₂ are in good agreement with observations, while those of CN, HCO⁺, CS and SiO are in rough agreement. The results indicate that molecular species such as CH, CH₂, CH₂⁺ , HCl, OH and H₂O are anticipated to be highly abundant in these objects.  相似文献   

The impact of spheroid stars for Macho microlensing surveys of the Andromeda galaxy     

Eamonn Kerins 《Monthly notices of the Royal Astronomical Society》2004,347(3):1033-1042

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Taking measure of the Andromeda halo: a kinematic analysis of the giant stream surrounding M31     

R. Ibata  S. Chapman  A. M. N. Ferguson  M. Irwin  G. Lewis  A. McConnachie 《Monthly notices of the Royal Astronomical Society》2004,351(1):117-124

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