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1.
The source IRAS 03134 + 5958 identified by Iyengar & Verma (1984) on the Palomar Observatory Sky Survey (POSS) prints with
a nonstellar optical object with [P – R]≃ 5.3 ± 1.5 is near the edge of Lynds dark cloud No. 1384 and is either embedded in or behind the cloud. The galactic latitude
of this source (b
II = 2‡.3), its positionvis-a-vis the Lynds dark cloud, its nonstellar appearance, high [P – R] colour and its far-infrared spectrum, all suggest the possibility of its being a Herbig-Haro (HH) object. To test this possibility
we undertook measurements of its proper motion and variability (two of the characteristic properties of HH objects). These
yield μa = (3.6 ± 2.3) arcsec/century and μδ= (−1.2 ± 2.0) arcsec/century for its proper motion. The source reveals large variation in brightness between 1950 and 1954.
Optical line studies of the source are required to confirm its classification as an HH object. 相似文献
2.
U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ18O behaves conservatively in the overall estuarine region. Isotopes of reactive elements, viz. 234Th and 210Po, are removed from the estuarine waters in <2 days and <1 month, respectively, which is due to high suspended matter (30–301 mg l−1). 228Ra and 226Ra are profusely released into the estuarine waters in the low to mid-salinity regions.As expected, the opposite trend is observed in the case of estuarine sediments and suspended matter. Reactive isotopes of Th, 210Pb and 210Po are enriched, whereas Ra isotopes are depleted with respect to their parent nuclides in the estuarine sediments and suspended matter. 232Th/Al ratio appears well suited to study the distribution and mixing of the bed load sediments of the Ganga–Brahmaputra (G–B) and the Hooghly rivers with those from other rivers on the Bay of Bengal floor. 相似文献
3.
B.L.K. Somayajulu R. Rengarajan D. Lal R.F. Weiss H. Craig 《Earth and Planetary Science Letters》1987,85(4)
Measurements of five cosmogenic32Si vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO2 extracted range from 2 to 54 g; the amounts of water from which SiO2 was extracted range between 540 kg and 270, 000 kg. In additon, SiO2 recovered from four surface particulate composites (64°N to 61°S) were also analyzed for32Si.32Si measurements were made by milking and counting the daughter activity, 32P. The net32P activities range from 0.7 to 6.8 cph; typical errors in measurements of the32P activities are 20–30%.The32Si concentrations vary from 0.6 dpm/106 kg of water in the North Atlantic surface waters to 235 dpm/106 kg at 400 m depth in the circumpolar waters. The vertical profiles of32Si at the five Atlantic stations approximately follow the Si profiles but the depth gradients are different. This would be expected also considering the in-situ release mechanisms due to dissolution and advection/diffusion from the bottom waters. Except for the circumpolar station 89, where the Si and32Si profiles show the effect of marked vertical mixing (nearly depth independent profiles), the profiles show the following features: (1) specific activities of32Si (32Si/SiO2 ratios) are lowest at intermediate depths, and (2) on an average the surface specific activities are higher, by 2–4 times, than the bottom water values. These data are consistent with generation of the highest specific activity32Si waters at the surface, where Si concentrations are lowest and precipitation adds cosmogenic32Si scavenged from the troposphere. Rapid removal of biogenic silica to the water-sediment interface, without much dissolution during transit, leads to the second regime of high32Si specific activities.The32Si inventories in the water column in the latitude belt 27°N-27°S are in the range (1–1.4) × 10−2 dpm32Si/cm2, which is consistent with the expected fallout of cosmogenic32Si. However, the32Si column inventories south of 40°S are higher by a factor of 5–7, whereas the corresponding Si inventories increase by only a factor of 3. This excess32Si in the Southern Ocean cannot be explained by direct fallout from the stratosphere or by melting of Antarctic snow and ice. Instead, this excess is maintained primarily by the southward deep-water transport of32Si dissolved from sinking particulates. 相似文献
4.
Vertical and temporal variations in the activities of234Th,210Po and210Pb have been measured, in both dissolved and paniculate phases, at several stations in the eastern Arabian Sea and north-central
Bay of Bengal. A comparative study allows us to make inferences about the particle associated scavenging processes in these
two seas having distinct biogeochemical properties.
A common feature of the234Th profiles, in the Arabian Sea and Bay of Bengal, is that the dissolved as well as total (dissolved + particulate) activity
of234Th is deficient in the surface 200 m with respect to its parent,238U. This gross deficiency is attributed to the preferential removal of234Th by adsorption onto settling particles which account for its net loss from the surface waters. The scavenging rates of dissolved234Th are comparable in these two basins. The temporal variations in the234Th-238U disequilibrium are significantly pronounced both in the Arabian Sea and Bay of Bengal indicating that the scavenging rates
are more influenced by the increased abundance of particles rather than their chemical make-up. In the mixed layer (0–50 m),
the scavenging residence time of234Th ranges from 30 to 100 days.
The surface and deep waters of both the seas show an enhanced deficiency of dissolved210Po relative to210Pb and that of210Pb relative to226Ra. The deficiencies of both210Po and210Pb in the dissolved phases are not balanced by their abundance in the particulate form indicating a net loss of both these
nuclides from the water column. The scavenging rates of210Po and210Pb are significantly enhanced in the Bay of Bengal compared to those in the Arabian Sea. The mean dissolved210Po/210Pb and210Pb/226Ra activity ratios in deep waters of the Bay of Bengal are ∼ 0.7 and 0.1, respectively, representing some of the most pronounced
disequilibria observed to date in the deep sea. The Bay of Bengal and the Arabian Sea appear to be the regions of most intense
particle moderated scavenging processes in the world oceans. This is evidenced by the gross disequilibria exhibited by the
three isotope pairs used in this study. 相似文献
5.
The228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg−1, two to three orders of magnitude higher than those of ocean waters and lake waters. However, the228Ra/226Ra activity ratios, (0.12–1.29) × 10−2, are in the range reported for the hydrosphere.The surface waters of the Dead Sea are enriched in228Ra by a factor of about three over the near-bottom waters. There is a factor of about two spatial variability in the mid-depth Ra concentrations at the two profile stations. The near-bottom228Ra gradients yield vertical eddy diffusivity coefficient (K) of 2.0 and 0.4 cm2 s−1 at profile locations 1 and 2 respectively. These values are comparable to those measured in oceans and lakes. 相似文献
6.
R.R. Daniel S.K. Ghosh K.V.K. Iyengar T.N. Rengarajan S.N. Tandon R.P. Verma 《Icarus》1982,49(2):205-212
We present far-infrared observations of Saturn in the wavelength band 76–116 μm, using a balloon-borne 75-cm telescope launched on 10 December 1980 from Hyderabad, India, when B′, the Saturnicentric latitude of the Sun, was 4°.3. Normalizing with respect to Jupiter, we find the average brightness temperature of the disk-ring system to be 90 ± 3° K. Correcting for the contribution from rings using experimental information on the brightness temperature of rings at 20 μm, we find TD, the brightness temperature of the disk, to be 96.9 ± 3.5° K. The systematic errors and the correction for the ring contribution are small for our observations. We, therefore, make use of our estimate of TD and earlier observations of Saturn when contribution from the rings was large and find that for wavelengths greater than 50 μm, there is a small reduction in the ring brightness temperature as compared to that at 20 μm. 相似文献
7.
An attempt is made to search for a consistent model to explain the electromagnetic spectrum of the Crab nebula (Tau A). It is assumed that there is a continuous injection of electrons at the centre of the nebula with an energy spectrumE
–1.54 as evidenced by radio data. This spectrum must steepen to a slope larger than 2 at some energyE
i
in order to ensure that the energy input into electrons remains finite. The spectrum must also steepen beyond an energyE
c
depending on the magnetic field because of synchrotron energy losses. Two types of models are considered: Class I, in which the whole nebula is characterised by a uniform magnetic field, and Class II, in which besides the general fieldH
0, small filamentary regions of strong fieldH
s
are postulated.In models of Class I, the best fit to the observed data is obtained whenE
t
>E
c
andH
05×10–4 gauss. However, this predicts a decrease in X-ray source size beyond 40 KeV. There are two possibilities of Class II model depending on the residence time of electrons in strong field regions being small or large. The former case explains the flattening in the optical spectrum.Experiments to distinguish between the various models are indicated.Presented at the International Conference on Cosmic Rays, Budapest, 1969. 相似文献
8.
A.D. Karnik S.K. Ghosh T.N. Rengarajan R.P. Verma 《Monthly notices of the Royal Astronomical Society》2001,326(1):293-302
High-resolution far-infrared observations of a large area of the star-forming complex RCW 106 obtained using the TIFR 1-m balloon-borne telescope are presented. Intensity maps have been obtained simultaneously in two bands centred around 150 and 210 μm. Intensity maps have also been obtained in the four IRAS bands using HIRES-processed IRAS data. From the 150- and 210-μm maps, reliable maps of dust temperature and optical depth have been generated. The star formation in this complex has occurred in five linear sub-clumps. Using the map at 210 μm, which has a spatial resolution superior to that of IRAS at 100 μm, 23 sources have been identified. The spectral energy distribution (SED) and luminosity of these sources have been determined using the associations with the IRAS maps. The luminosity distribution of these sources has been obtained. Assuming these embedded sources to be zero-age main-sequence stars and using the mass–luminosity relation for these, the power-law slope of the initial mass function is found to be −1.73±0.5 . This index for this very young complex is about the same as that for more evolved complexes and clusters. Radiation transfer calculations in spherically symmetric geometry have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR and the IRAS bands. From this, the r −2 density distribution in the envelopes is ruled out. Finally, a correlation is seen between the luminosity of embedded sources and the computed dust masses of the envelopes. 相似文献
9.
Samples of spiral galaxies from two catalogues of 21 cm line observations and a catalogue of near-infrared observations of
nearby galaxies have been used in conjunction with Infrared Astronomical Satellite data to study correlations involving MG, the dynamic mass of the galaxies, the luminosities in theH band (1.6Μm), the blue band and the far infrared bands and the mass of atomic hydrogen, it is found that both the blue and the far-IR
luminosities which are indicators of star formation averaged over ∼3 × l09 and ∼107 years respectively, have a linear dependence onM
G On the other hand, theH luminosity which is a measure of star formation averaged over the lifetime of galaxies, has a steeper power law dependence
onM
G. The correlations observed do not have significant dependence on the morophological type of the galaxies There is a poor correlation
between the far-infrared luminosity and the mass of atomic hydrogen. The mass of atomic hydrogen has a dependence of the formM
G. Because of the decrease in the mean mass for later morphological types and due to differences in power law dependences of
luminosities in different bands onM
G, the mean value of luminosity-to-mass ratio is a constant for blue and far-IR bands, decreases for theH band and the gas-to-mass ratio increases as morphological type increases. 相似文献
10.
Thermal internal boundary layer characteristics at a tropical coastal site as observed by a mini-SODAR under varying synoptic conditions 总被引：1，自引：0，他引：1
Thara V. Prabha R. Venkatesan Erich Mursch-Radlgruber G. Rengarajan N. Jayanthi 《Journal of Earth System Science》2002,111(1):63-77
Atmospheric boundary layer observations are conducted at a coastal site during a transition phase from winter to summer season
over the Indian peninsula. Thermal Internal Boundary Layer (TIBL) characteristics in presence of an off-shore and a weakly
influenced on-shore synoptic wind are examined with the help of measurements carried out with a mini-SODAR (SOund Detection
And Ranging), tethered balloon, and tower-based micrometeorological measurements. Influence of the changing synoptic scale
conditions on turbulent characteristics of TIBL is discussed.
Mini-SODAR data showed the development and decay of sea and land breeze. It is seen that the characteristics of TIBL over
the coastal land after sea breeze onset are similar to that of a shallow convective boundary layer (CBL) commonly found over
plain land. Inside the TIBL, a maximum wind speed was noted close to the surface due to the penetration of sea breeze. In
the off-shore case, a distinct sea breeze circulation was observed unlike in the case of on-shore flow. In the presence of
weak on-shore case, a ‘minor sea’ breeze is noted before the establishment of sea breeze and a reduction in the momentum fluxes
gives rise to decrease in the turbulence intensity. Updraft in the sea breeze front was stronger during weak synoptic conditions.
Influence of synoptic changes on the sea breeze-land breeze circulation such as onset, strength and duration of the sea-land
breeze are also examined.
This work was done while the first author was a visiting scientist at IGCAR, Kalpakkam, India. 相似文献