- ID:
- ivo://CDS.VizieR/VI/152
- Title:
- SOVAP-PICARD total solar irradiance
- Short Name:
- VI/152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From the SOlar VAriability PICARD (SOVAP) space-based radiometer, we obtained a new time series of the total solar irradiance (TSI) during Solar Cycle 24. Based on SOVAP data, we obtained that the TSI input at the top of the Earth's atmosphere at a distance of one astronomical unit from the Sun is 1361.8+/-2.4W/m^2^ (1{sigma}) representative of the 2008 solar minimum period. From 2010 to 2014, the amplitude of the changes has been of the order of +/-0.1%, corresponding to a range of about 2.7W/m^2^. To determine the TSI from SOVAP, we present here an improved instrument equation. A parameter was integrated from a theoretical analysis that highlighted the thermo-electrical non-equivalence of the radiometric cavity. From this approach, we obtained values that are lower than those previously provided with the same type of instrument. The results in this paper supersede the previous SOVAP analysis and provide the best SOVAP-based TSI-value estimate and its temporal variation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/531/A173
- Title:
- Spectroscopy of CaII-H line at solar limb
- Short Name:
- J/A+A/531/A173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present constraints on the thermodynamical structure of the chromosphere from ground-based observations of the CaII H line profile near and off the solar limb.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/19
- Title:
- Statistical analysis of solar active regions
- Short Name:
- J/ApJ/786/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The subsurface properties of active regions (ARs) prior to their appearance at the solar surface may shed light on the process of AR formation. Helioseismic holography has been applied to samples taken from two populations of regions on the Sun (pre-emergence and without emergence), each sample having over 100 members, that were selected to minimize systematic bias, as described in Paper I (Leka et al. 2013ApJ...762..130L). Paper II (Birch et al. 2013ApJ...762..131B) showed that there are statistically significant signatures in the average helioseismic properties that precede the formation of an AR. This paper describes a more detailed analysis of the samples of pre-emergence regions and regions without emergence based on discriminant analysis. The property that is best able to distinguish the populations is found to be the surface magnetic field, even a day before the emergence time. However, after accounting for the correlations between the surface field and the quantities derived from helioseismology, there is still evidence of a helioseismic precursor to AR emergence that is present for at least a day prior to emergence, although the analysis presented cannot definitively determine the subsurface properties prior to emergence due to the small sample sizes.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/91
- Title:
- Statistical studies of solar white-light flares
- Short Name:
- J/ApJ/851/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recently, many superflares on solar-type stars have been discovered as white- light flares (WLFs). The statistical study found a correlation between their energies (E) and durations ({tau}): {tau}{propto}E^0.39^, similar to those of solar hard/soft X-ray flares, {tau}{propto}E^0.2-0.33^. This indicates a universal mechanism of energy release on solar and stellar flares, i.e., magnetic reconnection. We here carried out statistical research on 50 solar WLFs observed with Solar Dynamics Observatory/HMI and examined the correlation between the energies and durations. As a result, the E-{tau} relation on solar WLFs ({tau}{propto}E^0.38^) is quite similar to that on stellar superflares ({tau}{propto}E^0.39^). However, the durations of stellar superflares are one order of magnitude shorter than those expected from solar WLFs. We present the following two interpretations for the discrepancy: (1) in solar flares, the cooling timescale of WLFs may be longer than the reconnection one, and the decay time of solar WLFs can be elongated by the cooling effect; (2) the distribution can be understood by applying a scaling law ({tau}{propto}E^1/3^B^-5/3^) derived from the magnetic reconnection theory. In the latter case, the observed superflares are expected to have 2-4 times stronger magnetic field strength than solar flares.
- ID:
- ivo://CDS.VizieR/J/ApJ/893/78
- Title:
- Streamer wave events from STEREO observations
- Short Name:
- J/ApJ/893/78
- Date:
- 03 Dec 2021 00:46:01
- Publisher:
- CDS
- Description:
- Transverse waves are sometimes observed in solar helmet streamers, typically after the passage of a coronal mass ejection (CME). The CME-driven shock wave moves the streamer sideways, and a decaying oscillation of the streamer is observed after the CME passage. Previous works generally reported observations of streamer oscillations taken from a single vantage point (typically the Solar and Heliospheric Observatory (SOHO) spacecraft). We conduct a data survey searching for streamer wave events observed by the COR2 coronagraphs on board the STEREO spacecraft. For the first time, we report observations of streamer wave events from multiple vantage points by using the COR2 instrument on both STEREO A and B, as well as the SOHO/LASCO C2+C3 coronagraphs. We investigate the properties of streamer waves by comparing the different events and performing a statistical analysis. Common observational features give us additional insight on the physical nature of streamer wave events. The most important conclusion is that there appears to be no relation between the speed of the CME and the phase speed of the resulting streamer wave, indicating that the streamer wave speed is determined by the physical properties of the streamer rather than the properties of the CME. This result makes streamer wave events excellent candidates for coronal seismology studies. From a comparison between the measured phase speeds and the phase speeds calculated from the measured periods and wavelengths, we could determine that the speed of the postshock solar wind flow in our streamers is around 300km/s.
- ID:
- ivo://CDS.VizieR/J/A+A/375/591
- Title:
- SUMER Spectral Atlas of Solar Disk Features
- Short Name:
- J/A+A/375/591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- List of spectral lines in the wavelength range from 668{AA} to 1611{AA} identified in SUMER (Solar Ultraviolet Measurements of Emitted Radiation, spectrograph on the spacecraft SOHO) spectra of the average quiet Sun (QS), a coronal hole (CH) and a sunspot on disk (SS). Spectral lines observed in second order of diffraction which are also given here, extend the lower wavelength limit to below 500{AA}. For each entry we give the observed wavelengths in angstrom, the identification, the transition, the peak of spectral radiance, L^peak^, in mW/(sr*m^2^*{AA}) (incl. background), and a cross-reference to other line lists available in the literature (cf., Sect. 5.1). For second-order lines radiance entries are generally not provided, since the background separation in both orders of diffraction is a non-trivial task, which can not be automated. Only a few radiance values of strong second-order lines with negligible first-order contribution are given, which are marked by an asterisk (*).
- ID:
- ivo://CDS.VizieR/J/ApJ/871/16
- Title:
- Sun active regions from 1976-2017
- Short Name:
- J/ApJ/871/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The purpose of this paper is to show that large active regions (ARs) with different magnetic configurations have different contributions to short-term and long-term variations of the Sun. As a case study, the complex {delta}-type AR12673 and the simple {beta}-type AR12674 are investigated in detail. Since the axial dipole moment at cycle minimum determines the amplitude of the subsequent cycle and space climate, we have assimilated the individual observed magnetic configurations of these two ARs into a surface flux transport model to compare their contributions to the axial dipole moment D. We find that AR12673 has a significant effect on D at the end of the cycle, making it weaker because of abnormal and complicated magnetic polarities. An initial strongly positive D ends up with a strongly negative value. The flare- poor AR12674 has a greater contribution to the long-term axial dipole moment than the flare-rich AR12673. We then carry out a statistical analysis of ARs larger than 800{mu}Hem (solar hemisphere) from 1976 to 2017. We use the flare index (FI) and define an axial dipole moment index (DI) to quantify the effects of each AR on space weather and space climate, respectively. Whereas the FI has a strong dependence on the magnetic configuration, the DI shows no such dependence. The DI is mainly determined by the latitudinal location and the latitudinal separation of the positive and negative magnetic fluxes of the ARs. Simple ARs have the same possibility as complex ARs to produce big DI values affecting space climate.
- ID:
- ivo://CDS.VizieR/J/ApJS/208/27
- Title:
- Sun and HD 84937 TiII log(gf) and abundances
- Short Name:
- J/ApJS/208/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Atomic transition probability measurements for 364 lines of Ti II in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer (FTS) and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies.
- ID:
- ivo://CDS.VizieR/J/A+A/552/A114
- Title:
- Sun chromospheric CaII-HK emission
- Short Name:
- J/A+A/552/A114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Monitoring of the photometric and chromospheric HK emission data series of stars similar to the Sun in age and average activity level showed that there is an empirical correlation between the average stellar chromospheric activity level and the photometric variability. In general, more active stars show larger photometric variability. Interestingly, the measurements and reconstructions of the solar irradiance show that the Sun is significantly less variable than indicated by the empirical relationship. We aim to identify possible reasons for the Sun to be currently outside of this relationship. We employed different scenarios of solar HK emission and irradiance variability and compared them with available time series of Sun-like stars.
- ID:
- ivo://CDS.VizieR/J/A+AS/110/351
- Title:
- Sun observations in 1992
- Short Name:
- J/A+AS/110/351
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of an observational campaign of the Sun are reported.
