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1.
O. White  G. Kopp  M. Snow  K. Tapping 《Solar physics》2011,274(1-2):159-162
Given the numerous ground-based and space-based experiments producing the database for the Cycle 23??C?24 Minimum epoch from September 2008 to May 2009, we have an extraordinary opportunity to understand its effects throughout the heliosphere. We use solar radiative output in this period to obtain minimum values for three measures of the Sun??s radiative output: the total solar irradiance, the Mg ii index, and the 10.7 cm solar radio flux. The derived values are included in the research summaries as a means to exchange ideas and data for this long minimum in solar activity.  相似文献   

2.
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   

3.
The relative Doppler velocities and linewidths in a polar coronal hole and the nearby quiet-Sun region have been obtained from the Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) observations using emission lines originating at different heights in the solar atmosphere from the lower transition region (TR) to the low solar corona. The observed region is separated into the network and the cell interior, and the behavior of the above parameters were examined in the different regions. It has been found that the histograms of Doppler velocity and width are generally broader in the cell interior than in the network. The histograms of Doppler velocities of the network and cell interior do not show significant differences in most cases. However, in the case of the quiet Sun, the Doppler velocities of the cell interior are more blueshifted than those of the network for the lowermost line He?ii 304 Å, and an opposite behavior is seen for the uppermost line Mg?ix 368 Å. The linewidth histograms show that the network–cell difference is more prominent in the coronal hole. The network has a significantly larger linewidth than the cell interior for the lowermost TR line He?ii 304 Å for the quiet Sun. For the coronal hole, this is true for the three lower TR lines: He?ii 304 Å, O?iii 599 Å, and O?v 630 Å. We also obtained the correlations between the relative Doppler velocity and the width. A mild positive correlation is found for the lowermost transition-region line He?ii 304 Å, which decreases even more or become insignificant for the intermediate lines. For the low coronal line Mg?ix 368 Å, the correlation becomes strongly negative. This might be caused by standing waves or waves propagating from the lower to the upper solar atmosphere. The results may have implications for the generation of the fast solar wind and coronal heating.  相似文献   

4.
Solar activity alternates between active and quiet phases with an average period of 11?years, and this is known as the Schwabe cycle. Additionally, solar activity occasionally falls into a prolonged quiet phase (grand solar minimum), as represented by the Maunder Minimum in the 17th century, when sunspots were almost absent for 70?years and the length of the Schwabe cycle increased to 14?years. To examine the consistency of the cycle length characteristics during the grand solar minima, the carbon-14 contents in single-year tree rings were measured using an accelerator mass spectrometer as an index of the solar variability during the grand solar minimum of the 4th century BC. The signal of the Schwabe cycle was detected with a statistical confidence level of higher than 95?% by wavelet analysis. This is the oldest evidence for the Schwabe cycle at the present time, and the cycle length is considered to have increased to approximately 16?years during the grand solar minimum of the 4th century BC. This result confirms the association between the increase of the Schwabe cycle length and the weakening of solar activity, and indicates the possible prolonged absence of sunspots in the 4th century BC as during the Maunder Minimum. Theoretical implications from solar dynamo theory are discussed in order to identify the trigger of prolonged sunspot absence. A possible association between the long-term solar variation around the 4th century BC and terrestrial cooling in this period is also discussed.  相似文献   

5.
The Maunder Minimum corresponds to a prolonged minimum of solar activity a phenomenon that is of particular interest to many branches of natural and social sciences commonly considered to extend from 1645 until 1715. However, our knowledge of past solar activity has improved significantly in recent years and, thus, more precise dates for the onset and termination of this particularly episode of our Sun can be established. Based on the simultaneous analysis of distinct proxies we propose a redefinition of the Maunder Minimum period with the core “Deep Maunder Minimum” spanning from 1645 to 1700 (that corresponds to the Grand Minimum state) and a wider “Extended Maunder Minimum” for the longer period 1618–1723 that includes the transition periods.  相似文献   

6.
We analyzed transient Ca ii H brightening associated with small-scale canceling magnetic features (CMFs) in the quiet Sun near disk center using Ca ii H filter images and Na D1 magnetograms of Hinode/SOT. We found that in most Ca ii brightening events related to CMFs the Ca ii H intensity peaks after the magnetic flux cancellation. Moreover, the brightening tends to appear as a pair of bright points of similar size and brightness overlying a magnetic bipole. Then a new opposite polarity fragment moves to them and cancels out. These results imply that magnetic reconnection takes place there and is responsible for CMFs.  相似文献   

7.
The Maunder Minimum is the period between 1645 and 1715. Its main characteristic is abnormally low and prolonged solar activity. However, some authors have doubted the low level of solar activity during that period by questioning the accuracy and objectivity of the observers. This work presents a particular case of a sunspot observed during the Maunder Minimum with an unusual shape of its umbra and penumbra: a hexagon. This sunspot was observed by Cassini in November 1676, just at the core of the Maunder Minimum. This historical observation is compared with a twin case that occurred recently in May 2016. The conclusion reached is that Cassini’s record is another example of the good quality of the observations that were made during the Maunder Minimum, showing the meticulousness of the astronomers of that epoch. This sunspot observation made by Cassini does not support the conclusions of Zolotova and Ponyavin (Astrophys. J. 800, 42, 2015) that professional astronomers in the seventeenth century only registered round sunspots. Finally, a discussion is given of the importance of this kind of unusual sunspot record for a better assessment of the true level of solar activity in the Maunder Minimum.  相似文献   

8.
The peculiar δ Del-variable ? Puppis (F6IIp) has been analysed on nine UV high-resolution spectra in the region of Mgii h- and k-lines. This analysis has shown: (1) The Mgii emission is present during the whole pulsation period and increases with increasing luminosity. Maximum emission fluxes seem to occur at phases 0.96–0.12. (2) The phase shift between intensity maxima of Caii and Mgii chromospheric emissions is probably about 0.26. Moreover, it seems that the phase shift between ? Pup and the Cepheid β Dor is longer for the Mgii emission (～0.44) than for the Caii one (～0.27). (3) Violet-red asymmetries are present in emission components. Moreover, the violet component K1V has always an intensity higher than the red one K1R. (4) The averaged radial velocity (RV) curve obtained from three metallic lines is in agreement with that obtained in the optical region. The RV curves of red emission and absorption components are rather similar to that of the metallic lines. Near the minimum of this RV curve, the chromospheric emissions show an intensity enhancement with a negative phase shift similar to that of light curve (～?30 deg). (5) A model with an emitting extended atmosphere around the star is proposed to explain an emission like feature in the self-reversed absorption component K3 and in K1.  相似文献   

9.
The Sun’s general magnetic field has shown polarity reversal three times during the last three solar cycles. We attempt to estimate the upcoming polarity reversal time of the solar magnetic dipole by using the coronal field model and synoptic data of the photospheric magnetic field. The scalar magnetic potential of the coronal magnetic field is expanded into a spherical harmonic series. The long-term variations of the dipole component ( $g^{0}_{1}$ ) calculated from the data of National Solar Observatory/Kitt Peak and Wilcox Solar Observatory are compared with each other. It is found that the two $g^{0}_{1}$ values show a similar tendency and an approximately linear increase between the Carrington rotation periods CR 2070 and CR 2118. The next polarity reversal is estimated by linear extrapolation to be between CR 2132.2 (December 2012) and CR2134.8 (March 2013).  相似文献   

10.
We present an investigation of line-of-sight (LOS) velocity oscillations in solar faculae and sunspots. To study the phase relations between chromospheric and photospheric oscillations of the LOS velocity, we measured the time lag of the chromospheric signal relative to the photospheric one for several faculae and sunspots in a set of spectral line pairs. The measured time lags are different for different objects. The mean measured delay between the oscillations in the five-minute band in faculae is 50?s for the Si?i 10?827?Å?–?He?i 10?830?Å pair; for the pair Fe?i 6569?Å?–?Hα 6563?Å the mean delay is 20?s; for the pair Fe?i 4551?Å?–?Ba?ii 4554?Å the mean delay is 7?s; for the pair Si?i 8536?Å?–?Ca?ii 8542?Å the mean delay is 20?s. For the oscillations in the three-minute band in sunspot umbrae the mean delay is 55?s for the Si?i 10?827?Å?–?He?i 10?830?Å pair; for the Fe?i 6569?Å?–?Hα 6563?Å pair it was not possible to determine the delay; for the Fe?i 4551?Å?–?Ba?ii 4554?Å pair the mean delay is 6?s; for the Si?i 8536?Å?–?Ca?ii 8542?Å pair the mean delay is 21?s. Measured delays correspond to the wave propagation speed, which significantly exceeds the generally adopted speed of sound in the photosphere. This raises the question of the origin of these oscillations. The possibility that we deal with slow MHD waves is not ruled out.  相似文献   

11.
Radiative lifetimes for excited states in La ii, Ce ii, Pr ii, Nd ii, Sm ii, Yb i, Yb ii, and Lu ii have been determined by means of the beam-foil technique or the zero-field level-crossing method. The lifetimes for La, Ce, Pr, Nd, Sm, and Yb are shorter than those computed by summing the transition probabilities of Corliss and Bozman by a factor of up to ~5. The large discrepancies between the abundance of La, Ce, Pr, Nd, and Sm in the solar photosphere and in meteorites are eliminated or greatly reduced if the abundance determinations of the solar photosphere are based upon the gf values of Corliss and Bozman, corrected for by the present lifetimes.  相似文献   

12.
Images taken in the band centered at 30.4 nm are routinely used to map the radiance of the He?ii Ly?α line on the solar disk. That line is one of the strongest, if not the strongest, line in the EUV observed in the solar spectrum, and one of the few lines in that wavelength range providing information on the upper chromosphere or lower transition region. However, when observing the off-limb corona, the contribution from the nearby Si?xi 30.3 nm line can become significant. In this work we aim at estimating the relative contribution of those two lines in the solar corona around the minimum of solar activity. We combine measurements from CDS taken in August 2008 with temperature and density profiles from semiempirical models of the corona to compute the radiances of the two lines, and of other representative coronal lines (e.g. Mg?x 62.5 nm, Si?xii 52.1 nm). Considering both diagnosed quantities from line ratios (temperatures and densities) and line radiances in absolute units, we obtain a good overall match between observations and models. We find that the Si?xi line dominates the He?ii line from just above the limb up to ≈?2?R ⊙ in streamers, while its contribution to narrowband imaging in the 30.4 nm band is expected to become smaller, even negligible in the corona beyond ≈?2?–?3?R ⊙, the precise value being strongly dependent on the coronal temperature profile.  相似文献   

13.
Mattig  W.  Nesis  A. 《Solar physics》1974,39(2):337-347
Observations of quiescent solar prominences with the Harvard College Observatory spectrometer abroad Skylab show that prominence material is optically thick in the Lyman alpha line and the Lyman continuum. The color temperature of the Lyman continuum has a mean of 6600 K and an upward gradient toward the top of the prominence. The departure coefficient of the ground state of hydrogen is found to be of the order of unity as expected from theory. The optical depth of the Ciii sheath region is determined directly from the observation of the limb through the prominence and used to infer the mean electron density and the temperature gradient of the sheath. The result implies that the sheath density is about 0.4, and the temperature gradient about 1.4 times the respective value in the Ciii transition zone of the quiet Sun. The Ciii triplet-singlet ratio for the prominence is found to give a density compatible, within the uncertainty of the atomic parameters, with the density obtained from the optical depth. The Oviλ1032 line, which is emitted by both the prominence and the surrounding corona, is used to obtain an estimate of the thickness of the outer transition sheath of the prominence.  相似文献   

14.
Si iv, C iv, and O vi resonance lines have been measured above quiet and active solar regions from both pointed OSO-8 instruments. From calibrated profiles, optical depths are computed with three different methods. All three methods provide evidence that the opacity above faculae is lower than above the quiet Sun. From lower and upper limits of the opacity, we derive limits of the electron density. Our first method assumes only that the source function is constant without any geometrical constraint. We find higher densities above faculae than above quiet regions (about a factor 10). A second method allows us to compute the density, temperature gradient and thickness of a plane-parallel model, for active and quiet Sun. Electron densities agree with those of the first method but they lie in the lower range of values previously determined from Skylab. This result can be explained by the moderate level activity of the observed faculae. Appendices give relevant elements of transfer theory and newly computed values of collisional rates.  相似文献   

15.
SWAP images from PROBA2 taken at 174 Å in the Fe ix/x lines are compared with simultaneous slitless flash spectra obtained during the solar total eclipse of 11 July 2010. Myriad faint low-excitation emission lines together with the He i and He ii Paschen α chromospheric lines are recorded on eclipse spectra where regions of limb prominences are obtained with space-borne imagers. We analyzed a deep flash spectrum obtained by summing 80 individual spectra to evaluate the intensity modulations of the continuum. Intensity deficits are observed and measured at the prominences boundaries in both eclipse and SWAP images. The prominence cavities interpreted as a relative depression of plasma density, produced inside the corona surrounding the prominences, and some intense heating occurring in these regions, are discussed. Photometric measurements are shown at different scales and different, spectrally narrow, intervals for both the prominences and the coronal background.  相似文献   

16.
14C abundance on the Earth can be modulated by both the solar wind and irradiance components of the solar cycle. The magnetic field component of the solar wind modulates 14C production whereas the irradiance component can result in a change in the exchange rate between the various reservoirs of the carbon biogeochemical cycle. The effects would be nearly synchronous and difficult to separate. The 0.1% amplitude of irradiance variation during the two most recent solar cycles is well known. A 22-yr cycle exists also in the measured global temperature record.We have divided the University of Washington high-precision data on14C in tree rings into three 91-yr intervals: AD 1540–1630, 1630–1720 and 1715–1805, before, during and after the Maunder Minimum. Unfortunately the AD 1540–1630 interval includes part of the Spörer Minimum as well as the intermediate interval of high solar activity. These data were analyzed by the DFT, MEM and MTM methods of spectral time series analysis. The ca. 22-yr cycle is prominent during the Maunder Minimum, whereas the 11-yr cycle is most prominent after the Maunder Minimum but totally suppressed during the Maunder Minimum. The lesser amplitude of the 11-yr cycle before the Maunder Minimum is most probably due to overlap with the Spörer Minimum.Vasiliev and Kocharov VK83 have previously suggested that the 22-yr cycle persists through the Maunder Minimum whereas the 11-yr cycle is suppressed. Our calculations show that irradiance forcing of the carbon cycle during the 11-yr cycle is negligible, so the observed 11-yr cycle in14 C must be the result of production rate changes. The presence of the 22-yr cycle and suppression of the 11-yr cycle during the Maunder Minimum is in accord with a model by Jokipii Jok91.  相似文献   

17.
We suggest from synoptic charts of radial magnetic field and intensities of spectral lines (Fe?i, He?ii, and Fe?ix/x) over Carrington rotations 1942??C?2050 that deep convective layers control the pattern of large-scale solar activity. A new result is a Kolmogorov-type energy spectrum of the longitudinal variations of solar activity. This spectrum for nonphotospheric scales of convection (harmonic number m<100) is a new ??fingerprint?? of turbulence in the deep layers of the solar convection zone (CZ). The manifestation of one source of convective turbulence in the deep CZ is revealed as the excess in the power spectrum over the Kolmogorov spectrum. This source may be identified with giant convection cells at the CZ bottom. The convective cascade of the turbulence starts at the vortex size corresponding to the trans-CZ convective cells with the turnover time which the mixing length theory (MLT) predicts. This connection between the MLT formalism and real features in the Sun could account for the success of the MLT in stellar modeling.  相似文献   

18.
A study of circumnuclear star-forming regions (CNSFRs) in several early-type spirals has been carried out in order to investigate their main properties: stellar and gas kinematics, dynamical masses, ionising stellar masses, chemical abundances and other properties of the ionised gas. Both high resolution (R～20,000) and moderate resolution (R～5000) have been used. In some cases, these regions (about 100–150 pc in size) are composed of several individual star clusters with sizes between 1.5 and 4.9 pc, estimated from Hubble Space Telescope images. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km?s?1, with the Hβ emission lines being narrower than both the stellar lines and the [Oiii]λ5007 Å lines. The twice ionised oxygen, on the other hand, shows velocity dispersions comparable to those of stars. We have applied the virial theorem to estimate dynamical masses of the clusters, assuming that the systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 107 to 108 M⊙ for the full CNSFRs. We obtain oxygen abundances which are comparable to those found in high-metallicity disc Hii regions from direct measurements of electron temperatures and consistent with solar values within the errors. The region with the highest oxygen abundance is R3+R4 in NGC3504, 12+log(O/H)=8.85, about 1.5 times solar. The derived N/O ratios are, on average, larger than those found in high-metallicity disc Hii regions, and they do not seem to follow the trend of N/O vs. O/H which marks the secondary behaviour of nitrogen. On the other hand, the S/O ratios span a very narrow range—between 0.6 and 0.8 times solar. Compared to high-metallicity disc Hii regions, CNSFRs show values of the O23 and the N2 parameters whose distributions are shifted to lower and higher values, respectively. Hence, even though their derived oxygen and sulphur abundances are similar, higher values would in principle be obtained for the CNSFRs if pure empirical methods were used to estimate abundances. CNSFRs also exhibit lower ionisation parameters than their disc counterparts, as derived from [Sii]/[Siii]. Their ionisation structure also seems to be different, with CNSFRs showing radiation-field properties more similar to Hii galaxies than to disc high-metallicity Hii regions.  相似文献   

19.
Spectrophotometric measurements of the nova-like variable RR Tel secured at Cerro Tololo in 1972 with a photoelectric spectrum scanner are compared with previously reported photographic measurements and some photoelectric spectrum scans obtained at Mt. Stromlo in 1961. We have attempted to use these data to calibrate the photographic measurements which had much higher spectral resolution. This effort is complicated by the change of the spectrum with time; [Fevii] and [Nev] seem to be increasing with respect to Hβ, while [Fevi], [oiii], and [Neiii] appear to be weakening.  相似文献   

20.
We present grids of stellar models and their associated oscillation frequencies that have been used by the CoRoT Seismology Working Group during the scientific preparation of the CoRoT mission. The stellar models have been calculated with the CESAM stellar internal structure and evolution code while the oscillation frequencies have been obtained from the CESAM models by means of the ADIPLS adiabatic oscillation programme. The grids cover a range of masses, chemical compositions and evolutionary stages corresponding to those of the CoRoT primary targets. The stellar models and oscillation frequencies are available on line through the Evolution and Seismic Tools Activity (ESTA) web site.  相似文献   

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