共查询到20条相似文献，搜索用时 125 毫秒
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K. P. Johns D. M. Cragg P. D. Godfrey & A. M. Sobolev 《Monthly notices of the Royal Astronomical Society》1998,300(4):999-1005
We investigate the possibility of interstellar masers in transitions of the methanol isotopomers CH3 OD, 13 CH3 OH and CH3 18 OH, and of CH3 SH. The model used, in which masers are pumped through the first and second torsionally excited states by IR radiation, has accounted successfully for the Class II masers in main species methanol, 12 CH3 16 OH. Several potential maser candidates are identified for CH3 OD, their detectability depending on the enrichment of this species in star-forming regions. In 13 CH3 OH and CH3 18 OH the best maser candidates are direct counterparts of the well-known 6.7- and 12.2-GHz methanol masers, but the lower interstellar abundance of these substituted species means that the expected brightness is greatly reduced. The maser candidates in CH3 SH are also weak. By comparing these species we find that the large b -component of the dipole moment in methanol plays a significant role in its propensity to form masers, as does the strong torsion–rotation interaction due to the light hydroxyl frame. Thus the exceptional brightness of interstellar methanol masers is due to a favourable combination of molecular properties as well as high interstellar abundance. 相似文献
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Chris Koen 《Monthly notices of the Royal Astronomical Society》2005,360(3):1132-1142
The results of more than 100 h of CCD photometric monitoring of 10 L dwarfs and two T dwarfs are presented. Reasonable evidence is shown for I C band variability in DENIS 0255−4700, DENIS 1705−0516 and 2M 2104−1037. Substantial brightening of the T dwarf binary ε Indi Bab was observed over the course of 3.6 h; it is unlikely that this could have been caused by surface spots. No unequivocal variability could be detected in the R C band. 相似文献
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Fernley Carney Skillen Cacciari & Janes 《Monthly notices of the Royal Astronomical Society》1998,293(3):L61-L64
We review the available observational data to show that the slope of the RR Lyrae MV –[Fe/H] relation is 0.18±0.03. The recent claim by Feast that, because of biases, the true slope is much steeper is not justified. 相似文献
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简要地回顾了Ｂｅ／Ｘ射线双星２０多年来在红外、可见光、紫外和Ｘ射线波段所取得的观测结果，着重介绍了多波段联合观测对探讨双星间的相互作用如中子星的吸积方式和Ｘ射线产生的原因等方面的意义，对这些观测结果的分析研究，将是人们了解Ｂｅ／Ｘ射线双星的轨道参数和双星的物理参数、建立理论模型的基础。 相似文献
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G. A. Galazutdinov J. Kreowski F. A. Musaev P. Ehrenfreund B. H. Foing 《Monthly notices of the Royal Astronomical Society》2000,317(4):750-758
The identity of the carriers of the diffuse interstellar bands (DIBs) is one of the most fascinating puzzles of modern spectroscopy. Over the last few years the number of known DIBs has grown substantially. In this paper we discuss the two recently discovered near-infrared weak interstellar features which have already been proposed as fingerprints of the buckminsterfullerene We present and discuss measurements of the two related DIBs within a larger sample of reddened targets, observed with different spectrometers, telescopes and site conditions. We provide additional arguments in favour of the interstellar origin of the two bands. We find evidence around the 9577-Å DIB of far-wing structures, which may affect broad-band measurements. We estimate corrections and errors for telluric and stellar blends, and show that the cores of the two DIBs are well correlated with a ratio near unity within 20 per cent. Finally, we discuss their relation to the laboratory spectra of and the search for two expected weaker transitions. 相似文献
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L. Cortese A. Boselli P. Franzetti R. Decarli G. Gavazzi S. Boissier V. Buat 《Monthly notices of the Royal Astronomical Society》2008,386(2):1157-1168
We investigate the dependence of the total-IR (TIR) to ultraviolet (UV) luminosity ratio method for calculating the UV dust attenuation A (UV) from the age of the underlying stellar populations by using a library of spectral energy distributions for galaxies with different star formation histories. Our analysis confirms that the TIR/UV versus A (UV) relation varies significantly with the age of the underlying stellar population: that is, for the same TIR/UV ratio, systems with low specific star formation rate (SSFR) suffer a lower UV attenuation than starbursts. Using a sample of nearby field and cluster spiral galaxies, we show that the use of a standard (i.e. age-independent) TIR/UV versus A (UV) relation leads to a systematic overestimate up to 2 mag of the amount of UV dust attenuation suffered by objects with low SSFR and in particular H i -deficient star-forming cluster galaxies. This result points out that the age-independent TIR/UV versus A (UV) relation cannot be used to study the UV properties of large samples of galaxies including low star-forming systems and passive spirals. Therefore, we give some simple empirical relations from which the UV attenuation can be estimated taking into account its dependence on the age of the stellar populations, providing a less biased view of UV properties of galaxies. 相似文献
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We present an analysis of the orientations of 1433 galaxies found in the region 15h 48m ≤α(2000) ≤ 19h 28m , −68°≤δ(2000) ≤−62° . In this region we investigated three Abell clusters (S0794, S0797, S0805) of richness Class 0 and the Triangulum Australis cluster. Our aim is to examine non-random effects in galaxy orientations in clusters. In addition, we classified the investigated galaxies into subsamples on the basis of their axial ratio, major diameter and morphology. The spin vector orientations of total galaxies in the investigated region is found to be random. No preferred orientation is found in the clusters. We could not note any morphological dependence of the galaxy orientations in our samples. No preferred orientations can be seen for the spiral galaxies. The morphologically unidentified galaxies, galaxies having major diameters of <47 arcsec, and the nearly edge-on galaxies ( b / a < 0.5, 0.4 < b / a ≤ 0.5) show anisotropy: spin vectors of galaxies tend to be oriented perpendicular to the Local Supercluster plane and spin vector projections tend to point radially with respect to the Virgo cluster centre. 相似文献
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K. I. Caputi R. J. McLure J. S. Dunlop M. Cirasuolo A. M. Schael 《Monthly notices of the Royal Astronomical Society》2006,366(2):609-623
We have selected and analysed the properties of a sample of 2905 Ks < 21.5 galaxies in ∼131 arcmin2 of the Great Observatories Origins Deep Survey (GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the evolution of Ks -selected galaxies with respect to the results already obtained in previous studies. We made use of the public deep multiwavelength imaging from the optical B through the infrared (IR) 4.5-μm bands, in conjunction with available spectroscopic and COMBO17 data in the CDFS, to construct an optimized redshift catalogue for our galaxy sample. We computed the Ks -band luminosity function and determined that its characteristic magnitude has a substantial brightening and a decreasing total density from z = 0 to 〈 z 〉= 2.5 . We also analysed the colours and number density evolution of galaxies with different stellar masses. Within our sample, and in contrast to what is observed for less massive systems, the vast majority (∼85–90 per cent) of the most massive ( M > 2.5 × 1011 M⊙ ) local galaxies appear to be in place before redshift z ∼ 1 . Around 65–70 per cent of the total assemble between redshifts z = 1 and 3 and most of them display extremely red colours, suggesting that plausible star formation in these very massive systems should mainly proceed in obscured, short-time-scale bursts. The remaining fraction (up to ∼20 per cent) could be in place at even higher redshifts z = 3–4 , pushing the first epoch of formation of massive galaxies beyond the limits of current near-IR surveys. 相似文献
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C. Koen T. Tanabé M. Tamura N. Kusakabe 《Monthly notices of the Royal Astronomical Society》2005,362(2):727-736
The M8.5 object SSSPM J0109−5101 has recently been shown to be both a periodic and a flaring variable, based on optical observations in the extreme red. More than 16 h of monitoring in the near-infrared (NIR) reported here failed to show any variability. Similarly, no NIR variability could be detected in intensive monitoring of three other suspected optical variables. This paper also reports on photometry of half a dozen targets monitored over a few weeks, and on the comparison of intensive monitoring at different epochs. In only one case, that of the T dwarf binary ε Indi Bab, is there good evidence for variability. Our results allow stringent limits to be placed on the NIR variability levels in a large sample of ultracool dwarfs. 相似文献
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H. Sugai R. I. Davies M. Ishii M. J. Ward 《Monthly notices of the Royal Astronomical Society》2000,317(2):447-452
We have obtained an H2 v =1–0 S(1) image of a merging galaxy system, NGC 6090, by using a Fabry–Perot imager. The H2 emission originates between the double nuclei of pre-merger galaxies, and exhibits an arc-like or ring-like structure almost connecting the double nuclei. This structure is similar to that suggested for Arp 220 from the velocity field measured by CO radio emission. The separation of the double nuclei in NGC 6090 is 5–6 arcsec, corresponding to a projected distance of 3–4 kpc. This is much larger than that of Arp 220 and suggests that the molecular gas distribution can form an organized shape between the nuclei, such as a ring, in a rather early phase of merging. 相似文献
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C. Codella R. Bachiller M. Benedettini P. Caselli 《Monthly notices of the Royal Astronomical Society》2003,341(2):707-716
The Cepheus A star-forming region has been investigated through a multiline H2 S and SO2 survey at millimetre wavelengths. Large-scale maps and high-resolution line profiles reveal the occurrence of several outflows. Cep A East is associated with multiple mass-loss processes: in particular, we detect a 0.6-pc jet-like structure which shows for the first time that the Cep A East young stellar objects are driving a collimated outflow moving towards the south.
The observed outflows show different clumps associated with definitely different H2 S/SO2 integrated emission ratios, indicating that the gas chemistry in Cepheus A has been altered by the passage of shocks. H2 S appears to be more abundant than SO2 in high-velocity clumps, in agreement with chemical models. However, we also find quite small H2 S linewidths, suggestive of regions where the evaporated H2 S molecules had enough time to slow down but not to freeze out on to dust grains. Finally, comparison between the line profiles indicates that the excitation conditions increase with the velocity, as expected for a propagation of collimated bow shocks. 相似文献
The observed outflows show different clumps associated with definitely different H