Bulletin of the Astronomical Society of India最新文献

Brown Dwarfs: The Missing Link Between Stars and Planets 褐矮星:恒星和行星之间缺失的一环

Bulletin of the Astronomical Society of India Pub Date : 2015-01-01 DOI: 10.1007/978-3-319-09894-4_4

S. Sengupta

引用次数: 1

Refractive Scintillation of Extragalactic Radio Sources 河外射电源的折射闪烁

Bulletin of the Astronomical Society of India Pub Date : 2008-06-16 DOI: 10.1063/1.37585

W. Coles

引用次数: 3

Solar control of ambient ionization of the ionosphere near the crest of the equatorial anomaly in the Indian zone 太阳对印度带赤道异常峰附近电离层环境电离的控制

Bulletin of the Astronomical Society of India Pub Date : 2008-02-04 DOI: 10.5194/ANGEO-26-47-2008

S. Chakraborty, R. Hajra

{"title":"Solar control of ambient ionization of the ionosphere near the crest of the equatorial anomaly in the Indian zone","authors":"S. Chakraborty, R. Hajra","doi":"10.5194/ANGEO-26-47-2008","DOIUrl":"https://doi.org/10.5194/ANGEO-26-47-2008","url":null,"abstract":"Long-term (1978-1990) total electron content (TEC) data have been analyzed to show the dependence of ambient ionization on EUV radiation from the Sun. TEC observations were made at Calcutta (22.58 N, 88.38 E ge- ographic, dip: 32 N), situated virtually below the north- ern crest of the equatorial ionization anomaly. Day-to-day changes in TEC at different local times do not show any sig- nificant correlation with F10.7 solar flux. A good correlation is, however, observed between the F10.7 solar flux and the monthly mean TEC when both are considered on a long-term basis, i.e. either in the ascending (1986-1990) or in the de- scending (1979-1985) phase. In the early morning hours the correlation coefficient maximizes around the 08:00-10:00 h IST interval. The flux independent nature of diurnal TEC is evident around the noon time hours of only a few months in the descending phase for F10.7 values greater than 150 unit. Variation of TEC for the whole time period (1979-1990) also exhibits a prominent hysteresis effect. The remarkable feature of the hysteresis effect is its local time dependence, leading to a temporal flip-over. Solar flux-normalized TEC values show a clear seasonal dependence with asymmetri- cal variations in the two equinoxes. The amplitudes of the equinoctial peaks reveal a prominent local time dependence. A further normalization leads to a typical local time varia- tion of TEC. Based on solar flux, seasonal and local time dependent features of TEC, an empirical formula has been developed to represent the TEC variation in the early morn- ing hours. It yields a quantitative estimate of the solar flux dependent nature of the TEC variation. The formula has been validated using the available TEC data and data from the neu- ral network.","PeriodicalId":50722,"journal":{"name":"Bulletin of the Astronomical Society of India","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2008-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.5194/ANGEO-26-47-2008","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70921236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 42

Broadband radio spectrum of SS433 SS433的宽带无线电频谱

Bulletin of the Astronomical Society of India Pub Date : 2006-01-01 DOI: 10.1051/0004-6361:20052755

S. Pal, S. Chakrabarti, A. Kraus, S. Mandal

{"title":"Broadband radio spectrum of SS433","authors":"S. Pal, S. Chakrabarti, A. Kraus, S. Mandal","doi":"10.1051/0004-6361:20052755","DOIUrl":"https://doi.org/10.1051/0004-6361:20052755","url":null,"abstract":"We obtained a broadband radio spectrum of the galactic compact object SS433 through the multi-wavelength campaign using the Giant Meter Radio Telescope (GMRT) and the Effelsberg 100-m Radio Telescope. The observations took place from 2005 January 03 to 2005 February 08 using eight different frequencies. We observed a flare which appeared to have started prior to January 18 and lasted till February 08. The light curves show a progressively larger time-delay as the radio frequency goes down. The peak of the 6 cm lightcurve is delayed by ∼ 3 days with respect to the peak of the 9mm lightcurve. There is an indication of the flattening of the spectrum and possibly a turnover at ∼ 1.5GHz. If we interpret this to be due to synchrotron self-absorption, the required magnetic field would become too large, however, free-free absorption by hot thermal surrounding medium formed due to stellar winds is still a possibility. All sky monitor (ASM) aboard Rossi X-ray Timing Experiment (RXTE) showed very high X-ray count on 2005 January 25 when the flare was well underway. This may be due to slamming of the radio ‘bullets’ with previously ejected, relatively slowly moving material.","PeriodicalId":50722,"journal":{"name":"Bulletin of the Astronomical Society of India","volume":"34 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1051/0004-6361:20052755","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"57813509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 3

Tracking pulsar dispersion measures using the Giant Metrewave Radio Telescope 使用巨型米波射电望远镜跟踪脉冲星色散测量

Bulletin of the Astronomical Society of India Pub Date : 2005-03-01 DOI: 10.1111/J.1365-2966.2005.08721.X

A. Ahuja, Y. Gupta, D. Mitra, A. Kembhavi

{"title":"Tracking pulsar dispersion measures using the Giant Metrewave Radio Telescope","authors":"A. Ahuja, Y. Gupta, D. Mitra, A. Kembhavi","doi":"10.1111/J.1365-2966.2005.08721.X","DOIUrl":"https://doi.org/10.1111/J.1365-2966.2005.08721.X","url":null,"abstract":"In this paper, we describe a novel experiment for the accurate estimation of pulsar dispersion measures (DMs) using the Giant Metrewave Radio Telescope. This experiment was carried out for a sample of 12 pulsars, over a period of more than one year (2001 January to 2002 May) with observations about once every fortnight. At each epoch, the pulsar DMs were obtained from simultaneous dual-frequency observations, without requiring any absolute timing information. The DM estimates were obtained from both the single-pulse data streams and from the average profiles. The accuracy of the DM estimates at each epoch is ∼1 part in 104 or better, making the data set useful for many different kinds of studies. \u0000 \u0000 \u0000 \u0000The time-series of DMs shows significant variations on time-scales of weeks to months for most of the pulsars. An analysis of the mean DM values from these data shows significant deviations from catalogue values (as well as from other estimates in the literature) for some of the pulsars, with PSR B1642−03 showing the most notable differences. From our analysis results it appears that the constancy of pulsar DMs (at the level of 1 in 103 or better) cannot be taken for granted. For PSR B2217+47, we see evidence of a large-scale DM gradient over a 1-yr period, which is modelled as being due to a blob of enhanced electron density sampled by the line of sight. For some pulsars, including pulsars with fairly simple profiles such as PSR B1642−03, we find evidence for small changes in DM values for different frequency pairs of measurement, a result that needs to be investigated in detail. Another interesting result is that we find significant differences in DM values obtained from average profiles and single-pulse data.","PeriodicalId":50722,"journal":{"name":"Bulletin of the Astronomical Society of India","volume":"357 1","pages":"1013-1021"},"PeriodicalIF":0.0,"publicationDate":"2005-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/J.1365-2966.2005.08721.X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62853661","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 15

FIP effect in RV Tauri stars. 金牛座RV星的FIP效应。

Bulletin of the Astronomical Society of India Pub Date : 2005-01-01 DOI: 10.1007/978-3-642-02859-5_90

K. R. Rao, B. E. Reddy

引用次数: 0

Measuring global curvature and cosmic acceleration with supernovae 用超新星测量全球曲率和宇宙加速度

Bulletin of the Astronomical Society of India Pub Date : 2002-01-01 DOI: 10.1088/0264-9381/19/13/307

B P Schmidt

引用次数: 0

The seismic sun 地震太阳

Bulletin of the Astronomical Society of India Pub Date : 2000-03-01 DOI: 10.1017/S007418090006109X

Sarbani Basu

引用次数: 5

A non-anthropic origin for a small cosmological constant 一个小的宇宙常数的非人类起源

Bulletin of the Astronomical Society of India Pub Date : 1999-11-10 DOI: 10.1142/S0217732399002443

C. Sivaram

引用次数: 8

Ionospheric effects of the total solar eclipse of 24 October, 1995 over Ahmedabad 1995年10月24日在艾哈迈达巴德的日全食对电离层的影响

Bulletin of the Astronomical Society of India Pub Date : 1997-01-01 DOI: 10.1016/S0273-1177(97)00789-8

H. Chandra, G. D. Vyas, S. Sharma

引用次数: 13