首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 312 毫秒
1.
Two quiescent solar prominences were observed in July 2000 from SUMER aboard SOHO and from the two German solar telescopes at Tenerife. Two‐dimensional images taken at the VTT simultaneously in the spectral lines Hβ at 4862 Å and Ca II at 8542 Å show no significant spatial variation of their pressure‐sensitive emission ratio. Slit spectra of the Ca II 8542 Å and He I 10830 Å lines obtained at the Gregory‐Coudé telescope yield 8000 K < Tkin < 9000 K and 3 km/s < Vn–th < 8 km/s. Among the various spectral ranges observed with SUMER, we first investigate the Lyman emission lines, which were fitted by Gaussians yielding reliable spectral radiances and line widths for the series members 5 < k < 18. A determination of the level population gives for the lower series members a Boltzmann temperature of 60 000 K, the higher members being over‐populated. This temperature indicates an origin of the Lyman lines from hot surroundings of the cool prominence body seen in the ground‐based data; this also holds for the ‘hotter’ SUMER lines.  相似文献   

2.
Analysis of spectral data of two neighboring infrared lines, Fe I 15648.5 Å (g = 3) and FeI 15652.9 Å (geff = 1.53) are carried out for a simple sunspot when it was near the solar disk center (μ = 0.92), to understand the basic structure of sunspot magnetic field. Inversions of Stokes profiles are carried out to derive different atmospheric parameters both as a function of location within the sunspot and height in the atmosphere. As a result of the inversion we have obtained maps of magnetic field strength, temperature, line‐of‐sight velocity, field inclination and azimuth for different optical depth layers between log(τ5) = 0 and log(τ5) = –2.0. In this paper we present few results from our inversion for a layer averaged between log(τ5) from 0.0 to –0.5.  相似文献   

3.
Zirconium (Zr), together with strontium and yttrium, is an important element in the understanding of the Galactic nucleosynthesis. In fact, the triad Sr‐Y‐Zr constitutes the first peak of s‐process elements. Despite its general relevance not many studies of the solar abundance of Zr were conducted. We derive the zirconium abundance in the solar photosphere with the same CO5BOLD hydrodynamical model of the solar atmosphere that we previously used to investigate the abundances of C‐N‐O. We review the zirconium lines available in the observed solar spectra and select a sample of lines to determine the zirconium abundance, considering lines of neutral and singly ionised zirconium. We apply different line profile fitting strategies for a reliable analysis of Zr lines that are blended by lines of other elements. The abundance obtained from lines of neutral zirconium is very uncertain because these lines are commonly blended and weak in the solar spectrum. However, we believe that some lines of ionised zirconium are reliable abundance indicators. Restricting the set to Zr II lines, from the CO5BOLD 3D model atmosphere we derive A (Zr) = 2.62 ± 0.06, where the quoted error is the RMS line‐to‐line scatter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
We have observed about 15 active regions on the Sun, with the Advanced Stokes Polarimeter and Dick Dunn Telescope at NSO/SP to map the Stokes parameters in the photospheric Fe 6302.5 Å and chromospheric Mg I 5173 Å lines, during 1999‐2002. The observations are corrected for dark current, gain, instrumental polarization and cross‐talk using ASP pipeline. The wavelength calibration is carried out using the O2 telluric line 6302 Å which is also present in the observations. The photospheric and chromospheric longitudinal magnetograms are made from the Stokes V profiles, which were intercalibrated with the Kitt Peak magnetograms. The plasma motions are inferred from the line bisector measurements at different positions of the spectral line. In this paper we present the height dependence of Doppler velocity scatter plots of a sunspot in the photospheric Fe I 6302 Å line.  相似文献   

5.
We discuss observations of the weak ?rst overtone (Δν = 2) CO absorption band near 2300 nm with the U.S. National Solar Observatory Array Camera (NAC), a modern mid‐infrared detector. This molecular band provides a thermal diagnostic that forms lower in the atmosphere than the stronger fundamental band near 4600 nm. The observed center‐to‐limb increase in CO line width qualitatively agrees with the proposed higher temperature shocks or faster plasma motions higher in the COmosphere. The spatial extent of chromospheric shock waves is currently at or below the diffraction limit of the available CO lines at existing telescopes. Five minute period oscillations in line strength and measured Doppler shifts are consistent with the p‐mode excitation of the photospheric gas. We also show recent efforts at direct imaging at 4600 nm. We stress that future large‐aperture solar telescopes must be teamed with improved, dynamic mid‐infrared instruments, like the NAC, to capitalize on the features that motivate such facilities (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
The GREGOR Fabry‐Pérot Interferometer (GFPI) is one of three first‐light instruments of the German 1.5‐meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large‐format, high‐cadence CCD detectors with sophisticated computer hard‐ and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field‐of‐view (FOV) of 50″×38″is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25″×38″. The spectral coverage in the spectroscopic mode extends from 530–860 nm with a theoretical spectral resolution of R ≈250 000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580–660 nm. The combination of fast narrow‐band imaging and post‐factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to ∼50 km on the solar surface (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
We experiment with a method of measuring the frequency of solar p modes, intended to extend the passband for the variations of the frequency spectrum as high as possible. So far this passband is limited to a fraction of μ Hz for the classical analysis based on numerical fits of a theoretical line profile to a power spectrum averaged over periods lasting at least several weeks. This limit for the present analysis can be shifted to the mHz range, corresponding to some of the “5 min” oscillations, but in this range we use a lower resolution which allows us to separate odd and even p modes. We show an example of the results for long term variations and apply this analysis to search for a modulation of the p‐mode frequency spectrum by asymptotic series of solar g modes. A faint signal is found in the analysis of 10 years of GOLF data. This very preliminary result possibly indicates the detection of a small number of g modes of degree l = 1. A tentative determination of an observational value of the parameter P0 follows. P0 is the scaling factor of the asymptotic series of g modes and is a key data for solar core physics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
The helioseismic instruments aboard the SOHO satellite make it possible to measure solar oscillations as variations of the irradiance (VIRGO) or as variations of the photospheric velocity (GOLF). Theoretically, phase differences between different photometric bands are expected to be around 0 degrees over the p‐mode frequency range. By using VIRGO (red) and VIRGO (blue) data, we find a mean phase shift of 8.05 ± 1.81°, whereas by using VIRGO (green) and VIRGO (blue) data, we got a mean value of –1.04 ± 0.19°. Hence, when the analysis includes the VIRGO infrared range, the Sun's atmosphere does not follow an exact adiabatic behavior. In this study, we use the phase shifts obtained by VIRGO (green) and VIRGO (blue) to determine the non‐adiabatic parameter phase lag (ψT) as a function of frequency. To this aim, we applied the non radial linearized formula put in the complex form by Garrido: we found a mean value of ψT = 179.95°. The lowest value being ψT = 179.90°, the departure from theoretical predictions is less then a tenth of a degree over the entire p mode frequency range. We can state that the solar atmosphere has a behavior close to the adiabatic case, when the phase shifts and amplitude ratios are computed using VIRGO (green) and VIRGO (blue) data. Nevertheless this small deviation is significant. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
The PICARD mission is a CNES micro‐satellite to be launched in 2009. Its goal is to better understand the Sun and the potential impact of its activity on earth climate by measuring simultaneously the solar total and spectral irradiance, diameter, shape and oscillations. We present the scientific objectives, instrumental requirements and data products of the helioseismology program of PICARD which aims to observe the low to medium l p‐mode oscillations in intensity and search for g‐mode oscillation signatures at the limb. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
The pulsation of the solar surface is caused by acoustic waves traveling in the solar interior. Thorough analyses of observational data indicate that these f and p helioseismic oscillation modes are not bounced back completely at the surface but they partially penetrate into the atmosphere. Atmospheric effects and their possible observational application are investigated in one‐dimensional magnetohydrodynamic models. It is found that f and p mode frequencies are shifted of the order of μHz due to the presence of an atmospheric magnetic field. This shift varies with the direction of the wave propagation.Resonant coupling of global helioseismic modes to local Alfvén and slow waves reduce the life time of the global modes. The resulting line width of the frequency line is of the order of nHz, and it also varies with propagation angle. These features enable us to use helioseismic observations in magnetic diagnostics of the lower atmosphere. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
Axial rotation of a star plays an important role in its evolution, physical conditions in its atmosphere and the appearance of its spectrum. We analyzed CCD spectra of nine stars for which the projected rotational velocity derived from the Ca II line at λ 3933 Å was remarkably lower than the one derived from the MgII line at λ 4481 Å. We derived effective temperatures and surface gravities using published uvbyβ photometries, and computed synthetic spectra. Comparing the observed line profiles of the two lines with the computed ones, we estimated the values of v sin i. One of the stars, HD44783, is a Be-star which, besides the narrow absorptions in the spectrum originating in its circumstellar envelope, also has lines of interstellar origin. We also found indications of circumstellar matter in the spectrum of HD25152. In the spectra of the remaining seven stars the narrow components in the Ca II λ 3933 Å line as well as narrow absorptions in the Na I λ 5889.951 Å (D1) and λ 5895.924 Å (D2) lines are of interstellar origin. In HD114376 there are two systems of interstellar components, thus disclosing two different interstellar clouds in the direction of the star. In the spectrum of HD138527 signs of a possible companion were detected, the emission of which contributes 15% to the total light of the system.  相似文献   

12.
We investigate the frequency dependence of the power spectral density of low-degree solar p modes by comparing measurements with the results of a stochastic-excitation model. In the past it was common practice to use the total power in such investigations. Using the maximum of the power spectral density instead provides a direct comparison with the measured mode heights in the observed power spectrum. This method permits a more careful calibration of the adjustable parameters in the excitation model, a model which we present here, for the first time, in a format that precisely and unambiguously relates the amplitudes of the modes of oscillation to the Reynolds stress in the equilibrium model. We find that errors in the theory of the linear mode damping rates, particularly at low frequency, have a dramatic impact on the predictions of the mode heights in the spectral density, whereas parameter changes in the stochastic excitation model, within a plausible domain of parameter space, have a comparatively small effect.  相似文献   

13.
This paper examines the way that transition region surface waves, generated in 2‐D numerical simulations of the nonmagnetic solar atmosphere when various synthetic photospheric drivers are applied, drive the granulation of the transition region/lower coronal region into convection cells. It is shown that these cells are generated by both synthetic point drivers and synthetic horizontally coherent p‐mode drivers. These cells cause the conversion of driven signals in vertical velocity into coronal signals predominantly in horizontal velocity, which if carried over to a case with a magnetic field included could cause mode conversion. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
This study based on longitudinal Zeeman effect magnetograms and spectral line scans investigates the dependence of solar surface magnetic fields on the spectral line used and the way the line is sampled to estimate the magnetic flux emerging above the solar atmosphere and penetrating to the corona from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO). We have compared the synoptic program λ5250 Å line of Fe?i to the line of Fe?i at λ5233 Å since this latter line has a broad shape with a profile that is nearly linear over a large portion of its wings. The present study uses five pairs of sampling points on the λ5233 Å line. Line profile observations show that the determination of the field strength from the Stokes V parameter or from line bisectors in the circularly polarized line profiles lead to similar dependencies on the spectral sampling of the lines, with the bisector method being the less sensitive. We recommend adoption of the field determined with the line bisector method as the best estimate of the emergent photospheric flux and further recommend the use of a sampling point as close to the line core as is practical. The combination of the line profile measurements and the cross-correlation of fields measured simultaneously with λ5250 Å and λ5233 Å yields a formula for the scale factor δ ?1 that multiplies the MWO synoptic magnetic fields. By using ρ as the center-to-limb angle (CLA), a fit to this scale factor is δ ?1=4.15?2.82sin?2(ρ). Previously δ ?1=4.5?2.5sin?2(ρ) had been used. The new calibration shows that magnetic fields measured by the MDI system on the SOHO spacecraft are equal to 0.619±0.018 times the true value at a center-to-limb position 30°. Berger and Lites (2003, Solar Phys. 213, 213) found this factor to be 0.64±0.013 based on a comparison using the Advanced Stokes Polarimeter.  相似文献   

15.
High precision center-limb spectrograms of the K i resonance doublet line at λ 7699 Å were used to study the line formation and to determine the abundance of potassium in the solar atmosphere. The LTE assumption is not valid for these lines. Synthetic profiles computed in NLTE reproduce very well the observed center-limb line behaviour and yield log? K = 5.14±0.10 for the solar abundance of potassium (on the scale of log? H = 12 for Hydrogen).  相似文献   

16.
A new method for the automated detection of coronal holes and filaments on the solar disk is presented. The starting point is coronal images taken by the Extreme Ultraviolet Telescope on the Solar and Heliospheric Observatory (SOHO/EIT) in the Fe ix/x 171 Å, Fe xii 195 Å, and He ii 304 Å extreme ultraviolet (EUV) lines and the corresponding full-disk magnetograms from the Michelson Doppler Imager (SOHO/MDI) from different phases of the solar cycle. The images are processed to enhance their contrast and to enable the automatic detection of the two candidate features, which are visually indistinguishable in these images. Comparisons are made with existing databases, such as the He i 10830 Å NSO/Kitt Peak coronal-hole maps and the Solar Feature Catalog (SFC) from the European Grid of Solar Observations (EGSO), to discriminate between the two features. By mapping the features onto the corresponding magnetograms, distinct magnetic signatures are then derived. Coronal holes are found to have a skewed distribution of magnetic-field intensities, with values often reaching 100?–?200 gauss, and a relative magnetic-flux imbalance. Filaments, in contrast, have a symmetric distribution of field intensity values around zero, have smaller magnetic-field intensity than coronal holes, and lie along a magnetic-field reversal line. The identification of candidate features from the processed images and the determination of their distinct magnetic signatures are then combined to achieve the automated detection of coronal holes and filaments from EUV images of the solar disk. Application of this technique to all three wavelengths does not yield identical results. Furthermore, the best agreement among all three wavelengths and NSO/Kitt Peak coronal-hole maps occurs during the declining phase of solar activity. The He ii data mostly fail to yield the location of filaments at solar minimum and provide only a subset at the declining phase or peak of the solar cycle. However, the Fe ix/x 171 Å and Fe xii 195 Å data yield a larger number of filaments than the Hα data of the SFC.  相似文献   

17.
Data collected recently by the helioseismic experiments aboard the SOHO spacecraft have allowed the detection of low degree p‐modes with increasingly lower order n. In particular, the GOLF experiment is currently able to unambiguously identify low degree modes with frequencies as low as 1.3 mHz. The detection of p‐modes with very low frequency (i.e., low n), is difficult due to the low signal‐to‐noise ratio in this spectral region and its contamination by solar signals that are not of acoustic origin. To address this problem without using any theoretical a priory, we propose a methodology that relies only on the inversion of observed values to define a spectral window for the expected locations of these low frequency modes. The application of this method to 2920‐day‐long GOLF observations is presented and its results discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
The spectral energy distributions between λ 3700 Å and λ 8100 Å of the binary systems COU1289 and COU1291 have been measured with the Carl‐Zeiss‐Jena 1 m telescope of the Special Astrophysical Observatory. Their B, V, R magnitudes and B – V colour indices were computed and compared with earlier investigations. Model atmospheres of both systems were constructed using a grid of Kurucz blanketed models, their spectral energy distributions in the continuous spectrum were computed and compared with the observational ones. The model atmosphere parameters for the components of COU1289 were derived as: T aeff = 7100 K, T beff = 6300 K, log g a = 4.22, log g b = 4.22, R a = 1.50 R⊙, R b = 1.40 R⊙, and for the components of COU1291 as: T aeff = 6400 K, T beff = 6100 K, log g a = 4.20, log g b = 4.35, R a = 1.47 R⊙, R b = 1.12 R⊙. The spectral types of both components of the system COU1289 were concluded as F1 and F7, and of the system COU1291 as F6 and F9. Finally the formation and evolution of the systems were discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
J. Koza 《Solar physics》2010,266(2):261-275
We examine the sensitivity of selected Ba?ii, Fe?i, Fe?ii, and Cr?i spectral lines to changes of the line-of-sight velocity by sharpness of their line profiles and response functions to line-of-sight velocity evaluated by the 1-D model of the quiet solar atmosphere in the LTE approximation. The set of selected lines includes the Ba?ii 4554 Å line, generally considered to be an excellent Doppler mapper. Our findings confirm earlier results showing that the sensitivity increases not only with wavelength, as anticipated from the Doppler relation, but mainly with the sharpness of line profiles given by the ratio of their depths and widths. The line Fe?i 5247 Å is the most sensitive in our set, whereas the Fe?i and Fe?ii infrared lines show very low sensitivity because of their large thermal widths. The line Ba?ii 4554 Å shows only moderate sensitivity due to its large width, given by a broad hyperfine structure and isotopic split. For the first time we identify a very promising and so far unknown Doppler mapper of the solar photosphere and low chromosphere, which is the line Ba?ii 6497 Å. Its sensitivity is comparable with the sensitivity of Fe?i 5247 Å and clearly surpasses the sensitivity of Ba?ii 4554 Å. The line Ba?ii 6497 Å offers many advantages, making it a highly recommendable choice for future studies of line-of-sight velocities in the photosphere and low chromosphere.  相似文献   

20.
Measurements of the solar diameter using both visual and photoelectric drift scan techniques have been made since 1972 using two almost identical 45‐cm Gregory‐Coudé telescopes at Locarno/Switzerland and Izaña/Tenerife. The method, in which a time measurement substitutes an angular measurement, is especially suited to obtain about 30 measurements of the absolute solar semidiameter per day. During the years 1972–2002 a total of 10996 visual timing measurements have been made on 320 observing days, an additional 1373 photoelectric recordings have been obtained on 117 observing days. The data were used to study the long‐term behaviour of the solar semidiameter R at unit distance and its possible variations. No fluctuations dR in excess of about ±0.05″ have been found, neither long‐term nor short‐term. The photoelectric semidiameter, which refers to the continuum at λ ≈ 585 nm, is Rphot = (959.89 ± 0.12)″. The visual semidiameter, which refers to the footpoint of the limb intensity profile at λ ≈ 550 nm, is Rvis = (960.62 ± 0.02)″.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号