In the last 30 days

• Open/close Robertson-Walker cosmological models with perfect fluid in general relativity

  Rishi Kumar Tiwari 2011 Res. Astron. Astrophys. 11 767 Tag this article

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  Einstein's field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for a Robertson-Walker universe by assuming the cosmological term to be proportional to R ^−m ( R is a scale factor and m is a constant). A variety of solutions is presented. The physical significance of the cosmological models has also been discussed.

• Open/close Physical origin of multi-wavelength emission of GRB 100418A and implications for its progenitor

  Lan-Wei Jia et al 2012 Res. Astron. Astrophys. 12 411 Tag this article

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  Swift GRB 100418A is a long burst at z = 0.624 without detection of any associated supernova (SN). Its light curves in both the prompt and afterglow phases are similar to GRB 060614, a nearby long GRB without an associated SN. We analyze the observational data of this event and discuss the possible origins of its multi-wavelength emission. We show that its joint light curve at 1 keV derived from Swift BAT and XRT observations is composed of two distinguished components. The first component, whose spectrum is extremely soft (Γ = 4.32), ends with a steep decay segment, indicating the internal origin of this component. The second component is a slowly-rising, broad bump which peaks at ~ 10 ⁵ s post the BAT trigger. Assuming that the late bump is due to onset of the afterglow, we derive the initial Lorentz factor (Γ0) of the GRB fireball and find that it significantly deviates from the relation between the Γ0 and isotropic gamma-ray energy derived from typical GRBs. We also check whether it follows the same anti-correlation between X-ray luminosity and the break time observed in the shallow decay phase of many typical GRBs, which is usually regarded as a signal of late energy injection from the GRB central engine. However, we find that it does not obey this correlation. We propose that the late bump could be contributed by a two-component jet. We fit the second component with an off-axis jet model for a constant medium density and find the late bump can be represented by the model. The derived jet half-opening angle is 0.30 rad and the viewing angle is 0.315 rad. The medium density is 0.05 cm ^-3, possibly suggesting that it may be from a merger of compact stars. The similarity between GRBs 060614 and 100418A may indicate that the two GRBs are from the same population and the late bump observed in the two GRBs may be a signal of a two-component jet powered by the GRB central engine.

• Open/close On the emission lines in active galactic nuclei with relativistic jets

  Luigi Foschini 2012 Res. Astron. Astrophys. 12 359 Tag this article

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  The effect of the observed continuum emitted from a relativistic jet on the measurement of the full width at half maximum (FWHM) of an emission line is analyzed. If the jet contribution is not properly subtracted, the FWHM of the line could seem narrower than it should. The cases of an emission line detected in BL Lac objects and γ-ray Narrow-Line Seyfert 1 galaxies (γ-NLS1s) are addressed. It is shown that the smallness of the observed FWHM of the Lyα lines detected in three well-known BL Lacs is an effect due to the combined action of both the relativistic jet and a weak accretion disk. Once the Doppler boosting effect of the jet continuum is removed, the intrinsic FWHM values of the lines are found to be in the usual range. By contrast, the narrow permitted lines in γ-NLS1s are really narrow, since the disk and the lines are much more powerful. This also confirms that γ-NLS1 is really a new class of γ-ray emitting AGN, different from blazars and radio galaxies.

• Open/close The relationships of solar flares with both sunspot and geomagnetic activity

  Zhan-Le Du and Hua-Ning Wang 2012 Res. Astron. Astrophys. 12 400 Tag this article

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  The relationships between solar flare parameters (total importance, time duration, flare index, and flux) and sunspot activity ( R _z) as well as those between geomagnetic activity ( aa index) and the flare parameters can be well described by an integral response model with the response time scales of about 8 and 13 months, respectively. Compared with linear relationships, the correlation coefficients of the flare parameters with R _z, of aa with the flare parameters, and of aa with R _z based on this model have increased about 6%, 17%, and 47% on average, respectively. The time delays between the flare parameters with respect to R _z, aa to the flare parameters, and aa to R _z at their peaks in a solar cycle can be predicted in part by this model (82%, 47%, and 78%, respectively). These results may be further improved when using a cosine filter with a wider window. It implies that solar flares are related to the accumulation of solar magnetic energy in the past through a time decay factor. The above results may help us to understand the mechanism of solar flares and to improve the prediction of the solar flares.

• Open/close A new photometric study of the triple star system EF Draconis

  Yuan-Gui Yang 2012 Res. Astron. Astrophys. 12 419 Tag this article

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  We present new charge-coupled device (CCD) photometry for the triple star EF Draconis, obtained in 2009 and 2011. Using the updated Wilson-Devinney program, the photometric solutions were deduced from two sets of light curves. The results indicate that EF Dra is an A-type W UMa binary with a contact degree of f = 46.7%(±0.6%) and a third light of l ₃ ≃ 1.5%. Through analyzing the O — C curve, it is found that the orbital period shows a long-time increase with a light-time orbit. The period, semi-amplitude and eccentricity of the third body are P _mod = 17.20(±0.18) yr, A = 0.0039 ^d(±0.0002 ^d) and e = 0.49(±0.02) respectively. This kind of tertiary companion may extract angular momentum from the central system. The orbital period of EF Dra secularly increases at a rate of dP/ dt = +3.72(±0.07) × 10 ^-7 d yr ^-1, which may be interpreted by mass transfer from the less massive to the more massive component. As period increases, the separation between components may increase, which will cause the contact degree to decrease. With mass transferring, the spin angular momentum will increase, while the orbital angular momentum will decrease. Only if the contact configuration would merge at could this kind of deep-contact binary with period increasing, such as EF Dra, evolve into a rapidly-rotating single star.

• Open/close Recent progress of solar physics research in China

  Cheng Fang 2011 Res. Astron. Astrophys. 11 1377 Tag this article

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  Owing to the largely improved facilities and working conditions, solar physics research in China has recently shown marked development. This paper reports on the recent progress of solar physics research in Mainland China, mainly focusing on several hot issues, including instrumentations, magnetic field observations and research, solar flares, filaments and their eruptions, coronal mass ejections and related processes, as well as active regions and the corona, small-scale phenomena, solar activity and its predictions. A vision of the future is also described.

• Open/close The new RS CVn binary V1034 Her revisited and the orbital period — activity relation of short-period RS CVn binaries using photometric distortion amplitude

  Li-Yun Zhang 2012 Res. Astron. Astrophys. 12 433 Tag this article

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  This paper presents new CCD BV RI light curves of the newly discovered RS CVn eclipsing binary V1034 Her in 2009 and 2010, the shapes of which are different from previously published results. They show an asymmetric outside eclipse, and we try to use a spot model to explain the phenomenon. Using the Wilson-Devinney program with a one-spot or two-spot model, photometric solutions of the system and starspot parameters were derived. Comparing the two results shows that the case of two spots is more successful in reproducing light-curve distortions. Looking at all the spot longitudes, the trend is towards active longitude belts and each active longitude belt may switch. Comparing the light curves from 2009 and 2010, we can see that the light curve changes over the long time scale of a year, especially in phase 0.25. In addition, we also collected the values of the maximum amplitudes of photometric distortion of the short-period RS CVn binary. We found for the first time that there is a trend of increasing activity with decreasing orbital period. Finally, fitting all available light minimum times including our newly obtained ones with a polynomial function confirmed that the orbital period of V1034 Her increased.

• Open/close Discovery of Balmer broad absorption lines in the quasar LBQS 1206+1052

  Tuo Ji et al 2012 Res. Astron. Astrophys. 12 369 Tag this article

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  We report the discovery of Balmer broad absorption lines (BALs) in the quasar LBQS 1206+1052 and present a detailed analysis of the peculiar absorption line spectrum. Besides the Mg II λλ2796, 2803 doublet, BALs are also detected in the He I* multiplet at λλ2946, 3189, 3889 Å arising from the metastable helium 2 ³ S level, and in Hα and Hβ from the excited hydrogen H I* n = 2 level, which are rarely seen in quasar spectra. We identify two components in the BAL troughs of Δυ ~2000 km s ⁻¹ width: One component shows an identical profile in H I*, He I* and Mg II with its centroid blueshifted by −υ _c ≈ 726 km s ⁻¹. The other component is detected in He I* and Mg II with − υ _c ≈ 1412 km s ⁻¹. We estimate the column densities of H I*, He I*, and Mg II, and compare them with possible level population mechanisms. Our results favor the scenario that the Balmer BALs originate in a partially ionized region with a column density of N _H ~ 10 ²¹ − 10 ²² cm ^-2 for an electron density of n _e ~ 10 ⁶ − 10 ⁸ cm ^-3 via Lyα resonant scattering pumping. The harsh conditions needed may help to explain the rarity of Balmer absorption line systems in quasar spectra. With an i-band PSF magnitude of 16.50, LBQS 1206+1052 is the brightest Balmer-BAL quasar ever reported. Its high brightness and unique spectral properties make LBQS 1206+1052 a promising candidate for follow-up high-resolution spectroscopy, multi-band observations, and long-term monitoring.

• Open/close ¹²CO, ¹³CO and C¹⁸O observations along the major axes of nearby bright infrared galaxies

  Qing-Hua Tan et al 2011 Res. Astron. Astrophys. 11 787 Tag this article

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  We present simultaneous observations of ¹²CO, ¹³CO and C ¹⁸O J = 1-0 emission in 11 nearby ( cz < 1000km s ⁻¹) bright infrared galaxies. Both ¹²CO and ¹³CO are detected in the centers of all the galaxies, except for ¹³CO in NGC 3031. We have also detected C ¹⁸O, CS J = 2−1 and HCO ⁺ J = 1−0 emission in the nuclear regions of M82 and M51. These are the first systematical extragalactic detections of ¹²CO and its isotopes from the PMO 14m telescope. We have conducted half-beam-spaced mapping of M82 over an area of 4' × 2.5' and major axis mapping of NGC 3627, NGC 3628, NGC 4631 and M51. The radial distributions of ¹²CO and ¹³ CO in NGC 3627, NGC 3628 and M51 can be well fitted by an exponential profile. The ¹²CO/ ¹³CO intensity ratio, , decreases monotonically with the galactocentric radius in all mapped sources. The average in the center and disk of the galaxies are 9.9±3.0 and 5.6±1.9, respectively, much lower than the peculiar (~24) found in the center of M82. The intensity ratios of ¹³CO/C ¹⁸O, ¹³CO/HCO ⁺ and ¹³CO/CS (either our or literature data) show little variation with galactocentric radius, in sharp contrast with the greatly varied . This supports the notion that the observed gradient in could be the result of the variations of the physical conditions across the disks. The H ₂ column density derived from C ¹⁸O shows that the Galactic standard conversion factor ( X-factor) overestimates the amount of the molecular gas in M82 by a factor of ~2.5. These observations suggest that the X-factor in active star-forming regions (i.e., nuclear regions) should be lower than that in normal star-forming disks and the gradient in can be used to trace the variations of the X-factor.

• Open/close Geology of Mars after the first 40 years of exploration

  Angelo Pio Rossi and Stephan van Gasselt 2010 Res. Astron. Astrophys. 10 621 Tag this article

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  The knowledge of Martian geology has increased enormously in the last 40 yr. Several missions orbiting or roving Mars have revolutionized our understanding of its evolution and geological features, which in several ways are similar to Earth, but are extremely different in many respects. The impressive dichotomy between the two Martian hemispheres is most likely linked to its impact cratering history, rather than internal dynamics such as on Earth. Mars' volcanism has been extensive, very long-lived and rather constant in its setting. Water was available in large quantities in the distant past of Mars, when a magnetic field and more vigorous tectonics were active. Exogenic forces have been shaping Martian landscapes and have led to a plethora of landscapes shaped by wind, water and ice. Mars' dynamical behavior continues, with its climatic variation affecting climate and geology until very recent times. This paper tries to summarize major highlights in Mars' Geology, and points to deeper and more extensive sources of important scientific contributions and future exploration.