共查询到20条相似文献，搜索用时 15 毫秒
1.
Donald F. Neidig Jr. 《Solar physics》1973,33(1):63-67
The brightness temperature curve of the quiet Sun at millimeter wavelengths suggests a possible inversion in the mid-millimeter range. Interpreting this as a result of an actual inversion in the chromospheric temperature structure, and example of a model chromoshere is presented whose calculated temperature curve exhibits such an inversion. This model is then tested for radial brightness distribution at millimeter wavelengths. Comparing the calculated distributions at 3.2 mm and 6 mm with eclipse measurements made with parabolic cylinders at 3.2 mm and 8.6 mm shows qualitative agreement, allowing for instrumental smoothing. It is conluded that a chromospheric temperature inversion, either actual or effective, could account for the inversion suggested by millimeter data and also the complex brightness distributions measured during eclipses with parabolic cylinders. 相似文献
2.
John P. Hagen Paul N. Swanson Robert W. Haas Fred L. Wefer Raymond W. Vogt 《Solar physics》1971,21(2):286-296
The 7 March, 1970 total solar eclipse was observed at wavelengths of 3.2 and 8.3 mm; the object being to use the knife edge of the Moon as it passed across the Sun to improve angular resolution on the Sun. This in turn would provide a radial brightness distribution of the Sun with an angular resolution of a few seconds of arc.Excellent eclipse curves were obtained at 3 mm; however, some external interference marred the 8 mm record near totality.The 8 mm brightness distribution is subject to some uncertainty, but tends to show limb brightening. The 3 mm brightness distribution shows a well defined complex limb brightening within about 1 arc min of the optical limb. The maximum brightening is approximately 30% above the average disc temperature. 相似文献
3.
W. R. F. Dent J. M. Torrelles † M. Osorio N. Calvet G. Anglada 《Monthly notices of the Royal Astronomical Society》2006,365(4):1283-1287
We present 7 mm and 3.5 cm wavelength continuum observations towards the Herbig AeBe star HD169142 performed with the Very Large Array (VLA) with an angular resolution of ≃1 arcsec. We find that this object exhibits strong (≃4.4 mJy), unresolved (≲1 arcsec) 7 mm continuum emission, being one of the brightest isolated Herbig AeBe stars ever detected with the VLA at this wavelength. No emission is detected at 3.5 cm continuum, with a 3σ upper limit of ≃0.08 mJy. From these values, we obtain a spectral index α≳ 2.5 in the 3.5 cm to 7 mm wavelength range, indicating that the observed flux density at 7 mm is most likely dominated by thermal dust emission coming from a circumstellar disc. We use available photometric data from the literature to model the spectral energy distribution (SED) of this object from radio to near-ultraviolet frequencies. The observed SED can be understood in terms of an irradiated accretion disc with low mass accretion rate, , surrounding a star with an age of ≃10 Myr. We infer that the mass of the disc is ≃0.04 M⊙ , and is populated by dust grains that have grown to a maximum size of 1 mm everywhere, consistent with the lack of silicate 10 μm emission. These features, as well as indications of settling in the wall at the dust destruction radius, led us to speculate that the disc of HD169142 is in an advanced stage of dust evolution, particularly in its inner regions. 相似文献
4.
We investigate the question of disk formation during the protostar phase. We build on the results of Keene and Masson (1990) whose analysis of L1551 showed the millimeter continuum emission comes from both an unresolved circumstellar component, i.e., a disk and an extended cloud core. We model the dust continuum emission from the cloud core and show how it is important at 1.3 mm but negligible at 2.7 mm. Combining new 2.7 mm Owens Valley Interferometer data of IRAS-Dense cores with data from the literature we conclude that massive disks are also seen toward a number of other sources. However, 1.3 mm data from the IRAM 30 m telescope for a larger sample shows that massive disks are relatively rare, occurring around perhaps 5% of young embedded stars. This implies that either massive disks occur briefly during the embedded phase or that relatively few young stars form massive disks. At 1.3 mm the median flux of IRAS-Dense cores is nearly the same as T Tauri stars in the sample of Beckwithet al. (1990). We conclude that the typical disk mass during the embedded phase is nearly the same or less than the typical disk mass during the T Tauri phase.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
5.
On November 1 and 2, 1968 two flares of importance 2b associated with the active region = S15°, L = 173° presented particular activity in the mm band. The outburst of November 1 in the mm wavelength band was of the gradual rise and fall type, while 24 hours later, the outburst of November 2 was of the sudden increase type with flux increase of the order of 4000 units. In the cm band the flare of November 1 produced a flux increase greater than in the mm band, while on November 2 the flare produced a series of outbursts with gradually increasing maxima, but much lower than the mm flux increase. It is reported that generally the peak flux decreases with increasing wavelength. The outburst of November 2 follows this rule but it is exactly the opposite for the sudden increase outburst produced by the November 1 flare. As to whether an increased brightness produces a higher mm or cm flux increase, available observations are not sufficient to make a firm statement. 相似文献
6.
Alberto Franceschini Paola Andreani & Luigi Danese 《Monthly notices of the Royal Astronomical Society》1998,296(3):709-720
We exploit observations at 1.25 mm with the ESO–SEST telescope of a southern galaxy sample, selected from the IRAS PSC and complete to S 60 =2 Jy, to derive the FIR and mm luminosity functions and the conditional probability distributions of FIR and mm luminosity of galaxies. The reliability of these estimates is ensured by the good observed correlation of the far-infrared and mm emissions. This detailed knowledge of the millimetric properties of galaxies is used to simulate the extragalactic sub-mm sky (background intensity, small-scale anisotropy signals and discrete source statistics), which is the target of a variety of ground-based and space observatories. We find, in particular, that a recent tentative detection of a sub-mm background would require, if confirmed, strong evolution with cosmic time of the galaxy long-wavelength emissivity. We finally discuss ways to test such evolution with present and forthcoming facilities: while emphasizing the difficulty of achieving this with large mm telescopes on the ground (because of the poor atmospheric conditions of current sub-mm sites), we mention an interesting opportunity with the long-wavelength camera on ISO . Preliminary results of deep surveys, both from space and from the ground, seem indeed to require excess emission in the past by dusty galaxies with respect to no-evolution predictions. 相似文献
7.
Bradley L. Jolliff Kaylynn M. Rockow Randy L. Korotev Larry A. Haskin 《Meteoritics & planetary science》1996,31(1):116-145
Abstract— Through analysis by instrumental neutron activation (INAA) of 789 individual lithic fragments from the 2 mm–4 mm grain-size fractions of five Apollo 17 soil samples (72443, 72503, 73243, 76283, and 76503) and petrographic examination of a subset, we have determined the diversity and proportions of rock types recorded within soils from the highland massifs. The distribution of rock types at the site, as recorded by lithic fragments in the soils, is an alternative to the distribution inferred from the limited number of large rock samples. The compositions and proportions of 2 mm–4 mm fragments provide a bridge between compositions of <1 mm fines, and types and proportions of rocks observed in large collected breccias and their clasts. The 2 mm–4 mm fraction of soil from South Massif, represented by an unbiased set of lithic fragments from station-2 samples 72443 and 72503, consists of 71% noritic impact-melt breccia, 7% incompatible-trace-element-(ITE)-poor highland rock types (mainly granulitic breccias), 19% agglutinates and regolith breccias, 1% high-Ti mare basalt, and 2% others (very-low-Ti (VLT) basalt, monzogabbro breccia, and metal). In contrast, the 2 mm–4 mm fraction of a soil from the North Massif, represented by an unbiased set of lithic fragments from station-6 sample 76503, has a greater proportion of ITE-poor highland rock types and mare-basalt fragments: it consists of 29% ITE-poor highland rock types (mainly granulitic breccias and troctolitic anorthosite), 25% impact-melt breccia, 13% high-Ti mare basalt, 31% agglutinates and regolith breccias, 1% orange glass and related breccia, and 1% others. Based on a comparison of mass-weighted mean compositions of the lithic fragments with compositions of soil fines from all Apollo 17 highland stations, differences between the station-2 and station-6 samples are representative of differences between available samples from the two massifs. From the distribution of different rock types and their compositions, we conclude the following: (1) North-Massif and South-Massif soil samples differ significantly in types and proportions of ITE-poor highland components and ITE-rich impact-melt-breccia components. These differences reflect crudely layered massifs and known local geology. The greater percentage of impact-melt breccia in the South-Massif light-mantle soil stems from derivation of the light mantle from the top of the massif, which apparently is richer in noritic impact-melt breccia than are lower parts of the massifs. (2) At station 2, the 2 mm–4 mm grain-size fraction is enriched in impact-melt breccias compared to the <1 mm fraction, suggesting that the <1 mm fraction within the light mantle has a greater proportion of lithologies such as granulitic breccias which are more prevalent lower in the massifs and which we infer to be older (pre-basin) highland components. (3) Soil from station 6, North Massif, contains magnesian troctolitic anorthosite, which is a component that is rare in station-2 South-Massif soils. (4) Compositional differences between poikilitic impact-melt breccias from the two massifs suggest broad-scale heterogeneity in impact-melt breccia interpreted by most investigators to be ejecta from the Serenitatis basin. We have found rock types not previously recognized or uncommon at the Apollo 17 site. These include (1) ITE-rich impact-melt breccias that are compositionally distinct from previously recognized “aphanitic” and “poikilitic” groups at Apollo 17; (2) regolith breccias that are free of mare components and poor in impact melt of the types associated with the main melt-breccia groups, and that, if those groups derive from the Serenitatis impact, may represent the pre-Serenitatis surface; (3) several VLT basalts, including an unusual very-high-K basaltic breccia; (4) orange-glass regolith breccias; (5) aphanitic-matrix melt breccias at station 6; (6) fragments of alkali-rich composition, including alkali anorthosite, and monzogabbro; (7) one fragment of 72275-type KREEP basalt from station 3; (8) seven lithic fragments of ferroan-anorthositic-suite rocks; and (9) a fragment of metal, possibly from an L chondrite. Some of these lithologies have been found only as lithic fragments in the soils and not among the large rock samples. In contrast, we have not found among the 2 mm–4 mm lithic fragments individual samples of certain lithologies that have been recognized as clasts in breccias (e.g., dunite and spinel troctolite). The diversity of lithologic information contained in the lithic fragments of these soils nearly equals that found among large rock samples, and most information bearing on petrographic relationships is maintained, even in such small samples. Given a small number of large samples for “petrologic ground truth,” small lithic fragments contained in soil “scoop” samples can provide the basis for interpreting the diversity of rock types and their proportions in remotely sensed geologic units. They should be considered essential targets for future automated sample-analysis and sample-return missions. 相似文献
8.
Albert Jambon 《Meteoritics & planetary science》2023,58(1):165-168
Matsui et al. (2022) performed X-ray fluorescence RF analyses of Tutankhamun's dagger and its hilt. Although the approach is indeed interesting, this work has many shortcomings. The absence of reference to standard specimens impairs both absolute values and error estimates, especially in chemical mapping. A Widmanstätten pattern at a scale of 1 mm cannot be revealed by chemical mapping with a step of 0.9 mm and spots exceeding significantly the 1 mm size. The presence of Ca on the hilt is probably an artifact as it can be observed on the blade and other objects as well. Finally, since the hilt and the blade may not be from the same origin, we have no clue about the origin of the dagger blade. 相似文献
9.
Titan has been observed with the 5-m Hale telescope at an effective wavelength of 1 mm. Adopting a value of 2700 km for the radius of Titan, we find a brightness temperature of 86±12°K at 1 mm. Comparing our results with previous measurements at longer wavelengths, we conclude that the satellite surface is the source of the 1-mm radiation. Since our measured brightness temperature is close to the equilibrium temperature of a blackbody at the distance of Saturn, we believe there is no significant greenhouse effect on Titan. 相似文献
10.
The CdZnTe array detector is a new type of semiconductor detector being rapidly developed in recent years. It possesses a high spatial resolution and a high energy resolution, and it can work at room temperatures. This paper describes the physical properties and working principle of the CdZnTe array detector, as well as the manufacturing technology, including the chip pretreatment, passivation, ohmic electrode preparation, array template selection, and array packaging technology (micro-interconnection). For evaluating the perfor-mance of the detector, the authors have developed successfully a 4 pixel×4 pixel CdZnTe array and an 8 pixel×8 pixel CdZnTe array (with the thicknesses of 5 mm and 2 mm, the pixel size of 2 mm×2 mm, and the gaps of 0.15 mm and 0.2 mm, respectively) in cooperation with the partner. A multi-channel electronic readout system based on the ASIC (Application Specific Integrated Circuit) chip is devel-oped independently for the charge measurement of the 4 pixel×4 pixel CdZnTe array. The energy spectra and corresponding energy resolutions of the 16 pixels are obtained with the 137Cs radiative source, among them the best resolution is 4.8%@662 kev. 相似文献
11.
The relationship between the flaring rates and 8.6 mm brightness temperatures of active regions has been analyzed. We find that as the 8.6 mm brightness temperature of an active region increases, a larger proportion of the energy released by the region in the form of flares is contained in progressively larger flares. At all temperatures subflares are the most frequent event. At intermediate and high temperatures about 10% of the events are flares of importance 1 or larger with flares of importance 2 or larger contributing an increasing fraction of these events as the brightness temperature increases. 相似文献
12.
《Meteoritics & planetary science》2017,52(9):1-1
Cover: Miller Range 07273 is a melt breccia related to H chondrites that has some anomalous features. This image, which covers an area approximately 0.37 mm tall and 0.41 mm wide, is an EBSD (electron back scatter diffraction) image of a deformed barred olivine chondrule in MIL 07273, with colors representing olivine crystal orientations (IPF‐z), and monochrome showing crystallinity (band contrast) in other grains. Data suggest the principal stress orientation was generally up‐down in this image, with deformation of olivine involving rotation around the <010> direction (see article by A. Ruzicka et al. on p. 1964). Image provided by A. Ruzicka. 相似文献
13.
Abstract— The Leedey, Oklahoma, meteorite shower fell on 1943 November 25, following a fireball which was visible across much of southwestern Oklahoma and northcentral Texas. The shower produced 24 stones with a total mass of ～51.5 kg. The stones formed a strewnfield ～18 km in length in the same direction as the observed path of the meteor (N50°W). Leedey is classified as an L6(S3) ordinary chondrite. We report bulk major element chemical analyses from four separate laboratories. Leedey contains an unusual 6 by 8 mm composite Fe,Ni-FeS grain, which is composed of a 3 mm kamacite grain adjacent to a 5 mm troilite grain. A 50–100 μm rim of high-Ni (45–55 wt%) taenite (tetrataenite) occurs at the boundary between kamacite and troilite. A single, zoned pyrophanite grain is observed at the boundary between the inclusion troilite and host silicates. An origin as a foreign particle incorporated after metamorphism or during impact melting appears unlikely. This particle likely formed by a complex set of processes, including melting in the nebula, parent body metamorphism and reheating by later shock, mirroring the history of the host chondrite. 相似文献
14.
Jeffrey L. Linsky 《Solar physics》1973,28(2):409-418
The solar millimeter continuum between 1 and 20 mm is recalibrated using observations of the average lunar brightness temperature at the center of lunar disk and new Moon brightness temperatures. The solar data are placed on a common scale according to the average lunar brightness temperature distribution proposed by Linsky. A least-squares parabolic regression curve is proposed for the solar millimeter continuum. A small departure from this regression curve near 8 mm may indicate the existence of an absorption feature.Staff member, Laboratory Astrophysics Division, National Bureau of Standards. 相似文献
15.
The TW Hydrae system is perhaps the closest analog to the early solar nebula. We have used the Very Large Array to image TW Hya at wavelengths of 7 mm and 3.6 cm with resolutions of 0&farcs;1 ( approximately 5 AU) and 1&farcs;0 ( approximately 50 AU), respectively. The 7 mm emission is extended and appears dominated by a dusty disk of radius greater than 50 AU surrounding the star. The 3.6 cm emission is unresolved and likely arises from an ionized wind or gyrosynchrotron activity. The dust spectrum and spatially resolved 7 mm images of the TW Hya disk are fitted by a simple model with temperature and surface density described by radial power laws, T&parl0;r&parr0;~r-0.5 and Sigma&parl0;r&parr0;~r-1. These properties are consistent with an irradiated gaseous accretion disk of mass approximately 0.03 M middle dot in circle with an accretion rate approximately 10-8 M middle dot in circle yr-1 and viscosity parameter alpha=0.01. The estimates of mass and mass accretion rates are uncertain since the gas-to-dust ratio in the TW Hya disk may have evolved from the standard interstellar value. 相似文献
16.
E. E. Reber 《Solar physics》1971,16(1):75-86
Absolute brightness temperatures and brightness temperature ratios of a quiet region near the center of the solar disk and the central region of the new moon were measured simultaneously at the 6 mm wavelength. The measured quiet sun/new moon brightness temperature ratios and reported central brightness temperatures of the new moon confirm the measured brightness temperature of the quiet sun at the 6 mm wavelength.Reported central brightness temperatures of the new moon are tabulated and graphed as a function of frequency and wavelength. The equation of a linear regression line for the reported measurements is given for estimating the brightness temperature of the new moon at any millimeter wavelength. Estimated brightness temperatures of the new moon and measured quiet sun/new moon ratios are used to estimate solar brightness temperatures at several millimeter wavelengths. The solar brightness temperatures, the regression line, and the Van de Hulst theoretical model are presented graphically as a function of frequency and wavelength. The regression line equation is given for estimating solar brightness temperatures at any wavelength in the 6 to 1 mm wavelength interval and is solved for the wavelength of the measured ratios.Reported solar brightness temperatures in the millimeter wavelength region are tabulated. The measured temperatures in the 6 to 1 mm wavelength interval and a linear regression line are presented graphically as a function of frequency and wavelength. The regression line equation is given and solved for the solar brightness temperatures at the 6 mm wavelength.This work supported by the U.S. Air Force under Contract No. F04701-69-C-0066. 相似文献
17.
Priscilla N Mohammed 《Icarus》2003,166(2):425-435
Recently, a model for the centimeter-wavelength opacity of PH3 under conditions characteristic of the outer planets was developed by Hoffman et al. (2001, PhD thesis), based on centimeter wavelength laboratory measurements. New laboratory measurements have been conducted which show that this model is also accurate at low pressures and temperatures, and at millimeter wavelengths such as will be employed in Cassini Ka-band (9.3 mm) radio occultation studies. The opacity of PH3 in a hydrogen/helium (H2/He) atmosphere has been measured at frequencies in the Ka-band region at 32.7 GHz (9.2 mm), 35.6 GHz (8.4 mm), 37.7 GHz (8.0 mm), and 39.9 GHz (7.5 mm) at pressures of 0.5, 1, and 2 bar and at temperatures of 295, 209, and 188 K. Additionally, new high-precision laboratory measurements of the opacity of NH3 in an H2/He atmosphere have been conducted under the same temperature and pressure conditions described for PH3. These new measurements better constrain the NH3 opacity model supporting use of a Ben-Reuven lineshape model. These measurements will also elucidate the interpretation of millimeter wavelength observations conducted with the NRAO/VLA at 43 GHz (7 mm). 相似文献
18.
The Bare Essentials of Surface Transfer (BEST) land surface scheme is briefly described and the key physical parameterisations discussed. Results are then presented to illustrate how the model performs, with forcing data for HAPEX-MOBILHY, compared to a series of other schemes in the simulation of evaporation and sensible heat. The implications of the models performance, and some indications of the future development of the scheme are provided. The basic version of BEST was found to overestimate evaporation for the HAPEX-MOBILHY data, simulating 816 mm yr−1 compared to a range of 550 to 816 mm yr−1 for all models. A modification to the β parameterisation reduced the evaporation to 759 mm yr−1 which, although an improvement, is still probably too high. 相似文献
19.
R. HOCHLEITNER K. T. FEHR G. SIMON J. POHL E. SCHMIDBAUER 《Meteoritics & planetary science》2004,39(10):1643-1648
Abstract— This study presents compositional data and 57Fe Mössbauer spectra, taken at 295 K and 85 K, of two fragments of the enstatite (EL6) chondrite Neuschwanstein that fell near the famous Neuschwanstein castle (Bavaria, southern Germany) on April 6, 2002. Main silicate minerals are enstatite (Fs 2) and plagioclase (An 20), the main opaque minerals are kamacite and troilite. Small amounts of oldhamite, daubreelite, and schreibersite have been found. The presented Mössbauer data are the first data gathered for an EL6 chondrite. The dominant parts of each Mössbauer spectrum consist of two six‐line patterns due to the presence of ferromagnetic phases kamacite and troilite. In contrast to other chondrites, peaks of other iron species in the central parts of the spectra are missing due to an extremely low content of Fe‐bearing paramagnetic components. The hyperfine interaction parameters for kamacite are internal magnetic hyperfine field Hhf = 333.2 kOe, isomer shift (relative to a metallic Fe foil) IS = 0.01 mm/s, quadrupole splitting QS = 0 mm/s, line width W = 0.41 mm/s. The data for troilite are Hhf = 305.5 kOe, IS = 0.75 mm/s, QS = ?0.85 mm/s, W = 0.34 mm/s. 相似文献