共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Ruiterkamp S. B. Charnley H. M. Butner H.-C. Huang S. D. Rodgers Y.-J. Kuan P. Ehrenfreund 《Astrophysics and Space Science》2007,310(3-4):181-188
We have observed emission from both ortho and para spin states of ketene (CH2CO) towards several deeply-embedded protostars. The low CH2CO fractional abundances (∼10−10) and the rotation temperatures (∼20 K) are consistent with emission from the cooler envelope. We compare our results with
previous studies and discuss possible production pathways to interstellar ketene. We suggest that, if low observed excitation
temperatures of CH2CO, CH3CHO and H2CO are indicative of their absence from the hot core region, then this may be due to the extensive hydrogenation of pre-existing
grain mantles prior to evaporation into the inner envelope, leading to lower abundances of these compounds and to mantles
rich in alcohols. 相似文献
2.
Theodore P. Snow Jr. 《Astrophysics and Space Science》1979,66(2):453-466
Observational results obtained to date on interstellar grains and molecules are briefly reviewed, and several promising areas for further research withSpacelab are suggested. Regarding grains, useful data can be expected on the shape of the ultraviolet extinction curve for new interstellar regions; the nature of UV extinction at short wavelengths, down to the Lyman limit; the presence or absence of structure in the UV extinction curve comparable to the visible-wavelength diffuse bands; the scattering properties of grains in new kinds of clouds and nebulae; and the polarization properties of grains in UV wavelengths. The principal advances which may be expected in observations of molecules will include the ability to probe more heavily-obscured regions, where molecular species are more abundant than in the diffuse clouds observed to date; coverage of wavelength regions (such as 1400–3200) not well-studied with previous instruments such asCopernicus; and the capability of observing in optical absorption species detected in the same line of sight in radio emission, which provides unique information on cloud geometry and physical conditions. 相似文献
3.
H. Vanhamäki 《Planetary and Space Science》2011,59(9):862-869
In the solar system all planets that have significant magnetic fields also emit electron cyclotron radiation, usually near the auroral regions around the magnetic poles. In this study we use scaling laws based on solar system data to estimate the power and frequency of the auroral cyclotron emissions from interstellar planets (or sub-brown dwarfs). The emission can be powered either by motion of the planet through the interstellar plasma or by unipolar induction due to a moon. According to our results, in interstellar space the unipolar induction mechanism is potentially more effective than the motional emission mechanism. Typical emission power is around 1010-1012 W, but significantly stronger emissions are obtained in the most optimistic estimates. We have to conclude that detection of a rogue Jupiter would be very difficult, if not impossible with the radio telescopes available now or in the near future, but in very favorable conditions a much more massive and rapidly rotating (or otherwise strongly magnetized) gas giant with a large nearby moon could be detected up to ∼57 pc distance with the square kilometer array. There may be a few thousand large enough interstellar planets this close to the solar system. For reference, we point out that according to previous studies some known hot Jupiters are expected to emit up to 1014-1016 W of cyclotron radiation, orders of magnitude more than the typical interstellar planets discussed here. However, these emissions have not yet been detected. 相似文献
4.
J. Meaburn 《Astrophysics and Space Science》1994,216(1-2):241-252
Complex motions are found over the shells which comprise the Honeycomb nebula. Evidence is presented for an episodic jet from Eta Carinae. The compact globules with radial spokes in the Helix nebula have both been shown to have dusty, molecular cores. Finally, highspeed flows of ionized gas are shown to be associated with the compact knots in the vicinity of the Trapezium cluster in the Orion nebula. 相似文献
5.
José F. Gómez Joaquín Trapero Carmen Morales Verónica Orozco Jerry Edelstein Eric Korpela Michael Lampton 《Astrophysics and Space Science》2001,276(1):233-238
EURD (EspectrógrafoUltravioleta extremo para la Radiación Difusa) is one of thescientific instruments on board MINISAT 01. EURD is a spectrograph withvery high sensitivity and spectral resolution ( 5 Å), designed to obtain extremeultraviolet ( 350-1100 Å) spectra of diffuse radiation.We outline the processing of EURD data, and how we obtain informationfrom these data on the scientific goals of the mission: hot interstellarmedium, neutrino decay line, nightglow emission, and early-type stars. 相似文献
6.
We present a detailed study of the bremsstrahlung gamma-ray emissivity of the galactic disk. We show that there are large uncertainties in the production spectrum of photons in the medium energy range (10–100 MeV) due to our lack of knowledge of the interstellar electron spectrum below a few hundred MeV. In fact, gamma-ray observations can be of great help in determining this spectrum. At present, the spectral shape of the local gamma-ray emissivity above 30 MeV is available, thanks to the SAS-II and the COS-B satellites. Comparing it to our calculations, we determine the local interstellar electron flux in the 50–500 MeV range; the corresponding integrated gamma-ray emissivity above 100 MeV is equal to 2.4×10–25 photons s–1 (H-atom)–1, 60% higher than previously accepted values. 相似文献
7.
8.
Shigeru Yoshioka 《Astrophysics and Space Science》1972,16(3):421-431
A re-analysis of the diffuse far UV radiation ( 1350–1480 Å) observed in the sky region ofl
II180° and 0°b
II40° is presented, as a revised version of a paper by Hayakawaet al. (1969). In comparison with the previous one, the value of the half optical depth of the Galazxy in our wavelength region is reduced, and the values of the albedo coefficient and the forward phase functiong are not well determined. If, however, we combine our results with the theoretical model of interstellar grains by Gilra, the value of is given by 0.13(5)0.18(5). 相似文献
9.
Carmen Morales José F. Gómez Joaquín Trapero Stuart Bowyer Jerry Edelstein Eric Korpela 《Astrophysics and Space Science》1998,263(1-4):393-396
EURD (Espectrógrafo Ultravioleta extremo de Radiación Difusa), one of the instruments onboard the Spanish satellite MINISAT-01,
is a spectrograph specially designed to detect diffuse radiation, covering the wavelength range of 350-1100 Å, with a spectral
resolution of 6-8 Å. Its main scientific objectives are the detection of the emission line spectrum from the hot phase of
the interstellar medium and the spectrum of the upper atmospheric airglow. In order to reduce geocoronal noise, EURD always
observes in the anti-sun direction and only when the satellite is in orbital eclipse. After more than one year of observation
we have obtained the best spectrum of the upper atmospheric nightglow in this wavelength range, the spectrum of 15 OB stars
and the spectrum of the full Moon throughout the year.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
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12.
From observations of interstellar Mgi, ii resonance lines, Gurzadyan has proposed recently that for the majority of hot stars most of the line-of-sight gas originates in dense, circumstellar clouds. To support this conclusion, which is contrary to most current models of the interstellar gas, he has set out apparently strong theoretical arguments based on empirical evidence from the sample of stars considered. In this paper we have considered the same data and have included some additional observations of interstellar Mg lines. We suggest that an empirical relationship between Mgii equivalent width and stellar effective temperature, which is central to the model proposed by Gurzadyan, may be explained by an observational selection effect. Further, we suggest that while circumstellar material may well contribute in part to observed column densities, there is no firm evidence that most of the gas is located in circumstellar clouds.Based in part on observations by the International Ultraviolet Explorer satellite collected at the Villafranca Tracking Station of the European Space Agency. 相似文献
13.
Barry Y. Welsh 《Astrophysics and Space Science》1983,90(2):437-444
High resolution optical observations (FWHM ~ 10–13 km s?1) of the I-S gas towards the early-type stars HD 164 794, HD 164816, and HD 165052 in the M8 Nebula are presented. A high velocity componentV LSR=?26 km s?1 has been detected in all 3 stars' spectra. A line profile fitting analysis has been carried out on the observed Caii and Nai absorption lines to determine cloud component column densities and to subsequently determine the physical and chemical conditions of the associated I-S gas. 相似文献
14.
15.
Rekhesh Mohan K. S. Dwarakanath G. Srinivasan Jayaram N. Chengalur 《Journal of Astrophysics and Astronomy》2001,22(1):35-50
Nearby interstellar clouds with high (|ν|≥10km s−1) random velocities although easily detected in NaI and CaII lines have hitherto not been detected (in emission or absorption)
in the HI 21cm line. We describe here deep Giant Metrewave Radio Telescope (GMRT) HI absorption observations toward radio
sources with small angular separation from bright O and B stars whose spectra reveal the presence of intervening high random
velocity CaII absorbing clouds. In 5 out of the 14 directions searched we detect HI 21cm absorption features from these clouds.
The mean optical depth of these detections is ∼0.09 and FWHM is ∼10km s−1, consistent with absorption arising from CNM clouds. 相似文献
16.
The diffuse far UV radiation ( 1350–1480 Å) observed in the sky region ofl
II180°, 0°b
II40° is analyzed in connection with the distributions of stars and dust grains as well as with optical properties of grains. Its intensity (starlight+scattered light) is about 6×10–7 erg cm–2 sec–1 sr–1 Å–1 in the direction ofb
II0° andl
II180°. The latitude dependence of the intensity is in approximate agreement with the plane parallel slab model of the galaxy with a reasonable set of parameters. The interstellar scattering gives an albedo close to unity and forward phase function of about 0.6, which are not inconsistent with the model of interstellar grains of Wickramasinghe. The upper limit of the extragalactic UV is 2×10–8 erg cm–2 sec–1 sr–1 Å–1 in the same region of wave-length. 相似文献
17.
K. S. Krishna Swamy 《Astrophysics and Space Science》1970,6(3):474-480
The expected intensity distribution of the infrared radiation in the solar neighborhood from the grain models of dirty ice, graphite and graphite core-dirty ice mantle has been calculated. It is found that the expected intensity from grain models at 100 agrees reasonably well with the observations of Hoffmann and Frederick. 相似文献
18.
José J. López-Moreno Carmen Morales José F. Gómez Joaquín Trapero Stuart Bowyer Jerry Edelstein Eric Korpela Michael Lampton 《Astrophysics and Space Science》2001,276(1):211-217
After 2 years of operation onboard the Spanish satellite MINISAT, EURDhas achieved an unprecedented success in the observation of the terrestrialnightglow in the EUV, covering a range of 350-1100 Å EURD hasprovided a total of more than 543 hours ofintegration in the long wavelength spectrometer and more than898 hours in the short wavelength one, allowing the achievement of the most detailed atlas of the terrestrial EUV nightglow ever obtained. We present here the spectra obtained, together with the identification of the lines, some of themdetected for the first time in the nightglow. These spectrarepresent an improvement in sensitivity of several orders of magnitude with respect to previous observations. It has beenpossible, for the first time, to identify the complete Lymanseries of atomic hydrogen, resolving up to Lyman-. It hasalso been possible to identify the helium Lyman- line at 537 Å andto detect other lines of the blended Lyman series of helium, at 515 and522 Å. The spectra clearly show the presenceof the OII lines at 617, 644, 673, and 718 Å, previouslyobserved in the dayglow but seen here for the first time in thenightglow. In addition to the recombination continuum of the atomicoxygen at 911 Å, two features of OI have been detected in thenightglow: the 3s 3Do transition at 989 Å, previouslyobserved by Chakrabarti (1984) and the 2p34s3So transition at 1040 Å, partially overlapped with Lyman , but clearly distinguishable from it. This feature has been seen for the first timein the terrestrial nightglow. The radiative recombination continuum of atomic oxygen at 911 Å, that wasabsent in the observations of the first year of operation of EURD,is now clearly visible. The reasons of the absence of the OIfeature during the first year of operation are still unknown.Anderson et al. (1976) also noticed a strong variation with time of this 911 Å emission. 相似文献
19.
R. Génova J. E. Beckman C. D. McKeith E. Barnett 《Astrophysics and Space Science》1990,171(1-2):235-238
We show here the first results of a programme of observations designed to probe the structure and kinematics of the Local Insterstellar Medium (LISM) using the Queen's University of Belfast Echelle Spectrograph (QUBES) on the 4.2 m William Herschel Telescope.The observations show the potential of the instrument for measuring small column densities, and for precise velocity structure analysis.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
20.
The UV radiation transfer within spherical interstellar dust clouds is analyzed using the method of successive scatterings. The results are used to determine the lifetime of interstellar H2CO against photo-destruction. The effectiveness of this process is compared with those of chemical mechanisms. 相似文献