共查询到20条相似文献,搜索用时 484 毫秒
1.
M. Shimojo T. S. Bastian A. S. Hales S. M. White K. Iwai R. E. Hills A. Hirota N. M. Phillips T. Sawada P. Yagoubov G. Siringo S. Asayama M. Sugimoto R. Brajša I. Skokić M. Bárta S. Kim I. de Gregorio-Monsalvo S. A. Corder H. S. Hudson S. Wedemeyer D. E. Gary B. De Pontieu M. Loukitcheva G. D. Fleishman B. Chen A. Kobelski Y. Yan 《Solar physics》2017,292(7):87
Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares. High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low-contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena. The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind. The requirements for solar observations are significantly different from observations of sidereal sources and special measures are necessary to successfully carry out this type of observations. We describe the commissioning efforts that enable the use of two frequency bands, the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum interferometric-imaging observations of the Sun with ALMA. Examples of high-resolution synthesized images obtained using the newly commissioned modes during the solar-commissioning campaign held in December 2015 are presented. Although only 30 of the eventual 66 ALMA antennas were used for the campaign, the solar images synthesized from the ALMA commissioning data reveal new features of the solar atmosphere that demonstrate the potential power of ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning efforts will continue to enable new and unique solar observing capabilities. 相似文献
2.
Rapid developments in the techniques of interferometry at millimeter wavelengths now permit the use of telescope arrays similar to the Very Large Array at microwave wavelengths. These new arrays represent improvements of orders of magnitude in the spatial resolution and sensitivity of millimeter observations of the Sun, and will allow us to map the solar chromosphere at high spatial resolution and to study solar radio burst sources at millimeter wavelengths with high spatial and temporal resolution. Here we discuss the emission mechanisms at millimeter wavelengths and the phenomena which we expect will be the focus of such studies. We show that the flare observations study the most energetic electrons produced in solar flares, and can be used to constrain models for electron acceleration. We discuss the advantages and disadvantages of millimeter interferometry, and in particular focus on the use of and techniques for arrays of small numbers of telescopes.Paper presented at the 4th CESRA Workshop in Ouranopolis (Greece) 1991. 相似文献
3.
C. L. Carilli F. Walter R. Wang A. Wootten K. Menten F. Bertoldi E. Schinnerer P. Cox A. Beelen A. Omont 《Astrophysics and Space Science》2008,313(1-3):307-311
We discuss observations of the first galaxies, within cosmic reionization, at centimeter and millimeter wavelengths. We present
a summary of current observations of the host galaxies of the most distant QSOs (z∼6). These observations reveal the gas, dust, and star formation in the host galaxies on kpc-scales. These data imply an enriched
ISM in the QSO host galaxies within 1 Gyr of the big bang, and are consistent with models of coeval supermassive black hole
and spheroidal galaxy formation in major mergers at high redshift. Current instruments are limited to studying truly pathologic
objects at these redshifts, meaning hyper-luminous infrared galaxies (L
FIR
∼1013
L
⊙). ALMA will provide the one to two orders of magnitude improvement in millimeter astronomy required to study normal star
forming galaxies (i.e. Ly-α emitters) at z∼6. ALMA will reveal, at sub-kpc spatial resolution, the thermal gas and dust—the fundamental fuel for star formation—in galaxies
into cosmic reionization. 相似文献
4.
P. J. Huggins 《Astrophysics and Space Science》2008,313(1-3):215-221
Our understanding of the late evolution of intermediate mass stars (∼1–8M⊙) through the planetary nebula phase is undergoing major developments. Observations at infrared and millimeter wavelengths
have revealed important components of neutral gas and dust in the nebulae that directly trace their formation from mass-loss
on the Asymptotic Giant Branch. At the same time, high resolution imaging, especially with the Hubble Space Telescope, has
revealed a surprising array of structures in the nebulae: multiple arcs, tori, jets, and myriads of small scale fragments.
None of these are fully understood, and all involve the neutral gas component. This paper highlights recent observations of
these structures and discusses the open questions, with an emphasis on those areas where observations with ALMA are likely
to make important contributions. 相似文献
5.
S. M. White K. Iwai N. M. Phillips R. E. Hills A. Hirota P. Yagoubov G. Siringo M. Shimojo T. S. Bastian A. S. Hales T. Sawada S. Asayama M. Sugimoto R. G. Marson W. Kawasaki E. Muller T. Nakazato K. Sugimoto R. Brajša I. Skokić M. Bárta S. Kim A. J. Remijan I. de Gregorio S. A. Corder H. S. Hudson M. Loukitcheva B. Chen B. De Pontieu G. D. Fleishmann D. E. Gary A. Kobelski S. Wedemeyer Y. Yan 《Solar physics》2017,292(7):88
The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at \(\lambda = 3~\mbox{mm}\) and 5900 K at \(\lambda = 1.3~\mbox{mm}\). These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of about \(25''\), the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range. Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool. Prominences above the solar limb are a common feature of the single-dish images. 相似文献
6.
A. Eckart T. Bertram N. Mouawad T. Viehmann C. Straubmeier J. Zuther 《Astrophysics and Space Science》2003,286(1-2):269-276
VLTI interferometry will allow imaging of galactic and extragalactic sources with milliarcsecond angular resolution. For moderately
bright sources the spectral resolution will be of the order of 10000. These capabilities will allow detailed studies of solar
system objects, stars, proto-planetary systems and the detection of hot extra-solar planets. The observations of galactic
nuclei will allow unprecedented measurements of physical parameters in these systems. VLTI will be a prime instrument to study
the immediate environment of the massive black hole at the center of the Milky Way. With the exception of a few `self-referencing'
sources the observations of extragalactic nuclei will benefit from an extended capability for simultaneous measurements of
nearby reference sources for fringe tracking. With beam combination instruments like AMBER, MIDI, PRIMA, and GENIE the VLTI
will reach full maturity at a time when other interferometric instruments at different wavelengths will be fully operational.
Most important are ALMA (in the mm- and sub-mm-domain), LOFAR and SKA (in the radio meter to centimeter domain) and of course
VLB-networks in the radio, and other – at that time –well developed interferometers in the optical. A major scientific potential
of future scientific VLTI programs will lie in an efficient combination of these high angular resolution capabilities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
The Atacama Large Millimeter/sub-millimeter Array (ALMA) is a large interferometer that will consist up to 64 high-precision antennas operating in the 31.3 – 950 GHz frequency
range. In this frequency range, which is largely unexplored, unique observations with a broad range of scientific objectives
(cosmology, cold universe, galaxies, stars and their formation, planets and so on) are expected. Among these tasks there is
a unique possibility to observe the Sun and to address several outstanding issues of solar physics. First, the ALMA is briefly
described and then the new ESO-ALMA European node (ARC), built at Ondřejov Observatory, is presented. In Europe, this ARC
is the only one oriented to solar physics. Consequently, the requirements and limitations for ALMA solar observations, as
well as some examples of possible solar-oriented ALMA projects, are shown. A procedure of the preparation and submission of
proposals for ALMA observations is mentioned. 相似文献
8.
Oliviero M. Moretti P.F. Severino G. Straus Th. Magrì M. Tripicchio A. 《Solar physics》2002,209(1):21-35
The intensity and velocity fluctuations, observed simultaneously, are a powerful diagnostic tool of the dynamics of the solar
atmosphere. The phase relation between the fluctuations can improve our knowledge of the solar background, its relation with
the acoustic sources, and its interaction with the solar acoustic oscillations. Furthermore, the opposite asymmetries observed
along the p-mode line profiles in the intensity and velocity power spectra contain information about the source of the solar acoustic
oscillations. For these reasons, it is relevant to study the height dependence of the asymmetries and phases in the solar
atmosphere. In this paper, we present the results from the analysis of observations performed by the VAMOS instrument in the
potassium 769.9 nm line and Na i D lines, and compare the measured phases with those obtained at different layers in the solar
atmosphere by different instruments, spanning from the base of the photosphere to the low chromosphere. 相似文献
9.
Satoko Takahashi Masao Saito Shigehisa Takakuwa Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):165-168
We have performed millimeter- and submilli- meter-wave survey observations using the Nobeyama millimeter array (NMA) and the
Atacama Submillimeter Telescope Experiment (ASTE) in one of the nearest intermediate-mass (IM) star-forming regions: Orion
Molecular Cloud-2/3 (OMC-2/3). Using the high-resolution capabilities offered by the NMA (∼several arcsec), we observed dust
continuum and H13CO+(1–0) emission in 12 pre- and proto-stellar candidates identified previously in single-dish millimeter observations. We unveiled
the evolutionary changes with variations of the morphology and velocity structure of the dense envelopes traced by the H13CO+(1–0) emission. Furthermore, using the high-sensitivity capabilities offered by the ASTE, we searched for large-scale molecular
outflows associated with these pre- and proto-stellar candidates observed with the NMA. As a result of the CO(3–2) observations,
we detected six molecular outflows associated with the dense gas envelopes traced by H13CO+(1–0) and 3.3 mm continuum emission. The estimated CO outflow momentum increases with the evolutionary sequence from early
to late type of the protostellar cores. We also found that the 24 μm flux increases as the dense gas evolutionary sequence.
We propose that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e. the CO outflow destroys the
envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential
role in the evolution of the IM protostars. The extremely high-sensitivity and high-angular resolution offered by ALMA will
reveal unprecedented details of the inner ∼50 AU of these protostars, which will provide us a break through in the classic
scenario of IM star/disk formation. 相似文献
10.
A. Vourlidas B. Sanchez Andrade-Nu?o E. Landi S. Patsourakos L. Teriaca U. Schühle C. M. Korendyke I. Nestoras 《Solar physics》2010,261(1):53-75
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding rocket payload built to study the crucial interface
between the solar chromosphere and the corona by observing the strongest line in the solar spectrum, the Ly α line at 1216 ?.
In two flights, VAULT succeeded in obtaining the first ever subarcsecond (
$0.5\hbox{$0.5\hbox{
) images of this region with high sensitivity and cadence. Detailed analyses of those observations contributed significantly
to new ideas about the nature of the transition region. Here, we present a broad overview of the Ly α atmosphere as revealed
by the VAULT observations and bring together past results and new analyses from the second VAULT flight to create a synthesis
of our current knowledge of the high-resolution Ly α Sun. We hope that this work will serve as a good reference for the design
of upcoming Ly α telescopes and observing plans. 相似文献
11.
T. L. Wilson 《Astrophysics and Space Science》2008,313(1-3):13-14
The Atacama Large Millimeter/submillimeter Array, ALMA, combines a large collecting area, very sensitive receivers and a location
on a high dry site. ALMA’s sensitivity for continuum measurements is increased with the added feature of an 8 GHz instantaneous
bandwidth. Taken together, these four factors provide unparalleled sensitivity in the millimeter/submillimeter wavelength
range. With its great sensitivity and angular resolution, ALMA will transform our view of mm/sub-mm astronomy. 相似文献
12.
Our aim is to test potential solar prominence plasma diagnostics as obtained with the new solar capability of the Atacama Large Millimeter/submillimeter Array (ALMA). We investigate the thermal and plasma diagnostic potential of ALMA for solar prominences through the computation of brightness temperatures at ALMA wavelengths. The brightness temperature, for a chosen line of sight, is calculated using the densities of electrons, hydrogen, and helium obtained from a radiative transfer code under non-local thermodynamic equilibrium (non-LTE) conditions, as well as the input internal parameters of the prominence model in consideration. Two distinct sets of prominence models were used: isothermal-isobaric fine-structure threads, and large-scale structures with radially increasing temperature distributions representing the prominence-to-corona transition region. We compute brightness temperatures over the range of wavelengths in which ALMA is capable of observing (0.32?–?9.6 mm), however, we particularly focus on the bands available to solar observers in ALMA cycles 4 and 5, namely 2.6?–?3.6 mm (Band 3) and 1.1?–?1.4 mm (Band 6). We show how the computed brightness temperatures and optical thicknesses in our models vary with the plasma parameters (temperature and pressure) and the wavelength of observation. We then study how ALMA observables such as the ratio of brightness temperatures at two frequencies can be used to estimate the optical thickness and the emission measure for isothermal and non-isothermal prominences. From this study we conclude that for both sets of models, ALMA presents a strong thermal diagnostic capability, provided that the interpretation of observations is supported by the use of non-LTE simulation results. 相似文献
13.
In this lecture, we review the properties of protoplanetary disks as derived from high angular resolution observations at millimeter wavelengths. We discuss how the combination of several different high angular resolution techniques allow us to probe different regions of the disk around young stellar objects and to derive the properties of the dust when combined with sophisticated disk models. The picture that emerges is that the dust in circumstellar disks surrounding pre-main sequence stars is in many cases significantly evolved compared to the dust in molecular clouds and the interstellar medium. It is however still difficult to derive a consistent picture and timeline for dust evolution in disks as the observations are still limited to small samples of objects.We also review the evidence for and properties of disks around high-mass young stellar objects and the implications on their formation mechanisms. The study of massive YSOs is complicated by their short lifetimes and larger average distances. In most cases high angular resolution data at millimeter wavelengths are the only method to probe the structure of disks in these objects.We provide a summary of the characteristics of available high angular resolution millimeter and submillimeter observatories. We also describe the characteristics of the ALMA observatory being constructed in the Chilean Andes. ALMA is going to be the world leading observatory at millimeter wavelengths in the coming decades, the project is now in its main construction phase with early science activities envisaged for 2010 and full science operations for 2012. 相似文献
14.
Nagayoshi Ohashi 《Astrophysics and Space Science》2008,313(1-3):101-107
Protoplanetary disks are the most probable sites where planet formation takes place. According to theory, planet formation
in protoplanetary disks should show remarkable signatures, such as a gap/hole or a spiral structure. In fact, recent high-angular
and high-sensitivity observations in millimeter and submillimeter wavelengths, as well as optical/near-IR wavelengths, have
shown such structures in protoplanetary disks. Two particular examples of such disks around AB Aurigae and HD 142527 are discussed
here, with an emphasis on results obtained using the Submillimeter Array. These disks—and their probable planet formation—will
be very important future targets for ALMA to study the physical process of planet formation in detail. 相似文献
15.
With modern imaging and spectral instruments observing in the visible, EUV, X-ray, and radio wavelengths, the detection of
oscillations in the solar outer atmosphere has become a routine event. These oscillations are considered to be the signatures
of a wave phenomenon and are generally interpreted in terms of magnetohydrodynamic (MHD) waves. With multiwavelength observations
from ground- and space-based instruments, it has been possible to detect waves in a number of different wavelengths simultaneously
and, consequently, to study their propagation properties. Observed MHD waves propagating from the lower solar atmosphere into
the higher regions of the magnetized corona have the potential to provide excellent insight into the physical processes at
work at the coupling point between these different regions of the Sun. High-resolution wave observations combined with forward
MHD modeling can give an unprecedented insight into the connectivity of the magnetized solar atmosphere, which further provides
us with a realistic chance to reconstruct the structure of the magnetic field in the solar atmosphere. This type of solar
exploration has been termed atmospheric magnetoseismology. In this review we will summarize some new trends in the observational
study of waves and oscillations, discussing their origin and their propagation through the atmosphere. In particular, we will
focus on waves and oscillations in open magnetic structures (e.g., solar plumes) and closed magnetic structures (e.g., loops and prominences), where there have been a number of observational highlights in the past few years. Furthermore, we
will address observations of waves in filament fibrils allied with a better characterization of their propagating and damping
properties, the detection of prominence oscillations in UV lines, and the renewed interest in large-amplitude, quickly attenuated,
prominence oscillations, caused by flare or explosive phenomena. 相似文献
16.
Tetsuo Hasegawa Takaaki Arai Nobuyuki Yamaguchi Fumio Sato 《Astrophysics and Space Science》2008,313(1-3):91-94
We report mapping observations of a 35 pc × 35 pc region covering the Sgr B2 molecular cloud complex in the 13CO (3-2) and the CS (7-6) lines using the ASTE 10 m telescope with high angular resolution. The central region was mapped
also in the C18O (3-2) line. The images not only reproduce the characteristic structures noted in the preceding millimeter observations,
but also highlight the interface of the molecular clouds with a large velocity jump of a few tens of km s−1. These new results further support the scenario that a cloud–cloud collision has triggered the formation of massive cloud
cores, which form massive stars of Sgr B2. Prospects of exciting science enabled by ALMA are discussed in relation to these
observations. 相似文献
17.
We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux
density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles.
We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we
use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance
and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second,
we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal
component exists and accounts for some of the variance in the data. This temporal component arises because active regions
with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative
and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative
flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux
density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the
chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures
of solar and stellar variability. 相似文献
18.
Amy J. Lovell 《Astrophysics and Space Science》2008,313(1-3):191-196
Thermal observations of large asteroids at millimeter wavelengths have revealed high amplitude rotational lightcurves. Such
lightcurves are important constraints on thermophysical models of asteroids, and provide unique insight into the nature of
their surface and subsurface composition. A better understanding of asteroid surfaces provides insight into the composition,
physical structures, and processing history of these surviving remnants from the formation of our solar system. In addition,
detailed observations of the larger asteroids, accompanied by thermophysical models with appropriate temporal and spatial
resolution, promise to decrease uncertainties in their flux predictions. Of particular interest are the near-Earth objects,
which can be observed at large phase angles, permitting better assessment of the thermal response of their unilluminated surfaces.
The high sensitivity of ALMA will enable us to detect many small bodies in all the major groups, to obtain lightcurves for
a large sample of main-belt and near-Earth objects, to resolve the surfaces of some large objects, and to separate the emission
from primary and secondary objects in binary pairs. In addition to the science goals of asteroid studies, these bodies may
also prove useful operationally because those with known shapes and well-characterized lightcurves could be employed for flux
calibration by ALMA and other high frequency instruments. 相似文献
19.
Spectral continua observed during solar flares may contain information about both thermal and non-thermal heating mechanisms.
Using two semi-empirical flare models F2 and FLA, we synthesize the thermal continua from optical to mm–radio domains and
compare their intensities with quiet-Sun values computed from a recent model C7. In this way, the far-infrared and sub-mm/mm
continua are studied for the first time, and we present our results as a benchmark for further modeling and for planning new
observations, especially with the ALMA instrument. Finally, we demonstrate how these continua are formed and show a close
correspondence between their brightness temperature and the kinetic-temperature structure of the flaring atmosphere. 相似文献
20.
Massimo Tarenghi 《Astrophysics and Space Science》2008,313(1-3):1-7
The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international millimeter-wavelength radio telescope under construction
in the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation which provides
excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key
observing components—a main array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging
in size from 0.15 to ∼18 km, and a set of four 12-m and twelve 7-m antennas operating in a compact array ∼50 m in diameter
(known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity
dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two
flexible digital correlators.
At the shortest planned wavelength and largest configuration, the angular resolution of ALMA will be 0.005″. The instrument
will use superconducting (SIS) mixers to provide the lowest possible receiver noise contribution, and special-purpose water
vapor radiometers to assist in calibration of atmospheric phase distortions. A complex optical fiber network will transmit
the digitized astronomical signals from the antennas to the correlators in the Array Operations Site Technical Building, and
post-correlation to the lower-altitude Operations Support Facility where the array will be controlled, and initial construction
and maintenance of the instrument will occur. ALMA Regional Centers in the US, Europe, Japan and Chile will provide the scientific
portals for the use of ALMA; early science observations are expected in 2010, with full operations in 2012. 相似文献