- ID:
- ivo://CDS.VizieR/J/ApJ/836/185
- Title:
- SEDs of the radio continuum from KINGFISHER
- Short Name:
- J/ApJ/836/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the spectral energy distribution (SED) of the radio continuum (RC) emission from the Key Insight in Nearby Galaxies Emitting in Radio (KINGFISHER) sample of nearby galaxies to understand the energetics and origin of this emission. Effelsberg multi-wavelength observations at 1.4, 4.8, 8.4, and 10.5GHz combined with archive data allow us, for the first time, to determine the mid-RC (1-10GHz, MRC) bolometric luminosities and further present calibration relations versus the monochromatic radio luminosities. The 1-10GHz radio SED is fitted using a Bayesian Markov Chain Monte Carlo technique leading to measurements for the nonthermal spectral index (S_{nu}_~{nu}^-{alpha}_nt_^) and the thermal fraction (f_th_) with mean values of {alpha}_nt_=0.97+/-0.16 (0.79+/-0.15 for the total spectral index) and f_th_=(10+/-9)% at 1.4GHz. The MRC luminosity changes over ~3 orders of magnitude in the sample, 4.3x10^2^L_{sun}_<MRC<3.9x10^5^L_{sun}_. The thermal emission is responsible for ~23% of the MRC on average. We also compare the extinction-corrected diagnostics of the star-formation rate (SFR) with the thermal and nonthermal radio tracers and derive the first star-formation calibration relations using the MRC radio luminosity. The nonthermal spectral index flattens with increasing SFR surface density, indicating the effect of the star-formation feedback on the cosmic-ray electron population in galaxies. Comparing the radio and IR SEDs, we find that the FIR-to-MRC ratio could decrease with SFR, due to the amplification of the magnetic fields in star-forming regions. This particularly implies a decrease in the ratio at high redshifts, where mostly luminous/star-forming galaxies are detected.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/891/79
- Title:
- Single storms and the related ICMEs from 1998-2011
- Short Name:
- J/ApJ/891/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interplanetary coronal mass ejections (ICMEs) could be classified into magnetic clouds (MCs) and non-MCs according to their magnetic field signatures, and into prominence-inside ICMEs (PIs) and non-PIs based on whether they contain colder and higher helium abundance plasmas than the solar wind. It is known that the MCs often lead to magnetic storms. However, whether or not the PIs have significant geoeffectiveness is unclear. This statistical work studies the southward interplanetary magnetic field (IMF) magnitude of the PIs, and the related magnetic storms' level. The data include the IMF and plasma moments measured by ACE and WIND, and the Dst index from 1998 to 2011. The hypothesis test based on the proportions of two groups is used to analyze 95 ICMEs related to single storms (SSs). The results show that the magnetic storms caused by the PIs mostly distribute at a strong level, while that caused by the non-PIs and by all the 95 ICMEs mostly distribute at a moderate level. The PIs have a significantly higher probability of generating SSs than the non-PIs. Moreover, the MCs containing carbon-cold and helium-enhanced materials (MC&PIs) have the highest fraction of minimum Bz, less than -11 nT. Since the MC&PIs have large-scale magnetic flux rope and prominence material, the stronger southward IMF is probably provided by the prominence. It is in accordance with the observed injection of enhanced twisted flux ropes to prominence. Therefore, the detailed eruption and propagation processes of the three-part coronal mass ejections deserve more concern from a space weather perspective.
- ID:
- ivo://CDS.VizieR/J/ApJS/239/12
- Title:
- Small-scale magnetic flux ropes in the solar wind
- Short Name:
- J/ApJS/239/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have developed a new automated small-scale magnetic flux ropes (SSMFR) detection algorithm based on the Grad-Shafranov (GS) reconstruction technique. We have applied this detection algorithm to the Wind spacecraft in situ measurements during 1996-2016, covering two solar cycles, and successfully detected a total number of 74241 small-scale magnetic flux rope events with duration from 9 to 361min. This large number of small-scale magnetic flux ropes has not been discovered by any other previous studies through this unique approach. We perform statistical analysis of the small-scale magnetic flux rope events based on our newly developed database, and summarize the main findings as follows. (1) The occurrence of small-scale flux ropes has strong solar-cycle dependency with a rate of a few hundred per month on average. (2) The small-scale magnetic flux ropes in the ecliptic plane tend to align along the Parker spiral. (3) In low-speed (<400km/s) solar wind, the flux ropes tend to have lower proton temperature and higher proton number density, while in high-speed (>=400km/s) solar wind, they tend to have higher proton temperature and lower proton number density. (4) Both the duration and scale size distributions of the small-scale magnetic flux ropes obey a power law. (5) The waiting time distribution of small-scale magnetic flux ropes can be fitted by an exponential function (for shorter waiting times) and a power-law function (for longer waiting times). (6) The wall-to-wall time distribution obeys double power laws with the break point at 60 minutes (corresponding to the correlation length). (7) The small-scale magnetic flux ropes tend to accumulate near the heliospheric current sheet (HCS).
- ID:
- ivo://CDS.VizieR/J/A+A/539/A13
- Title:
- Solar bipolar magnetic fields
- Short Name:
- J/A+A/539/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The area asymmetry between the preceding and following regions of opposite magnetic polarity in a bipolar sunspot group has been known since the studies of Hale and his colleagues in the early 20th century. This area asymmetry, however, has not yet been investigated quantitatively using magnetograms. We quantitatively define the area asymmetry of bipolar magnetic fields in the photosphere of active regions on the Sun, and investigate correlations between the area asymmetry and other parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A73
- Title:
- Solar Twins age-chromospheric activity
- Short Name:
- J/A+A/619/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1-2Gyr that is followed by a relatively inactive constant phase. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. We measured the CaII H and K activity indices using 9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (S_MW_), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Te, and then computed an improved bolometric flux normalized activity index logR'_HK_(Teff) for the entire sample. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using logR'_HK_(Teff). We measured an average solar activity of S_MW_=0.1712+/-0.0017 during solar magnetic cycles 23-24 covered by HARPS observations, and we also inferred an average of S_MW_=0.1694+/-0.0025 for cycles 10-24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6-7Gyr, in agreement with previous works using open clusters and field stars with precise ages. Our research confirms that CaII H& K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6-7Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations eects. The Sun seems to have a normal activity level and variability for its age.
- ID:
- ivo://CDS.VizieR/J/other/Ap/46.234
- Title:
- Spatial distribution of magnetic CP stars
- Short Name:
- J/other/Ap/46.23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of analysis of original publications and our own measurements a Cataloque of magnetic chemically peculiar (CP) upper-main sequence stars has been established. The sample includes 211 magnetic CP stars with magnetic fields ranging from hundreds of gauss to dozens of kilogauss, for 49 of them the surface magnetic field (B_e_) has been measured from the Zeeman splitting. The CP stars may be divided into 3 groups: reversing stars (table3, longitudinal field B_e_ changes its sign), non-reversing (table4, B_e_ keeps the same sign), and poorly studied stars.
- ID:
- ivo://CDS.VizieR/J/A+A/659/A35
- Title:
- Spectra of IRAS 17449+2320
- Short Name:
- J/A+A/659/A35
- Date:
- 04 Mar 2022 00:58:00
- Publisher:
- CDS
- Description:
- We report the first detection of the magnetic field in a star of FS CMa type, a subgroup of objects characterized by the B[e] phenomenon. The split of magnetically sensitive lines in IRAS 17449+2320 determines the magnetic field modulus of 6.2+/-0.2kG. Spectral lines and their variability reveal the presence of a B-type spectrum and a hot continuum source in the visible. The hot source confirms GALEX UV photometry. Because there is a lack of spectral lines for the hot source in the visible, the spectral fitting gives only the lower temperature limit of the hot source, which is 50000K, and the upper limit for the B-type star of 11100K. The V/R ratio of the Halpha line shows quasiperiodic behavior on timescale of 800 days. We detected a strong red-shifted absorption in the wings of Balmer and OI lines in some of the spectra. The absorption lines of helium and other metals show no, or very small, variations, indicating unusually stable photospheric regions for FS CMa stars. We detected two events of material infall, which were revealed to be discrete absorption components of resonance lines. The discovery of the strong magnetic field together with the Gaia measurements of the proper motion show that the most probable nature of this star is that of a post-merger object created after the leaving the binary of the birth cluster. Another possible scenario is a magnetic Ap star around Terminal-Age Main Sequence (TAMS). On the other hand, the strong magnetic field defies the hypothesis that IRAS 17449+2320 is an extreme classical Be star. Thus, IRAS 17449+2320 provides a pretext for exploring a new explanation of the nature of FS CMa stars or, at least, a group of stars with very similar spectral properties.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/49
- Title:
- Spectropolarimetric survey of radio sources
- Short Name:
- J/ApJ/815/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a broadband spectropolarimetric survey of 563 discrete, mostly unresolved radio sources between 1.3 and 2.0 GHz using data taken with the Australia Telescope Compact Array. We have used rotation-measure synthesis to identify Faraday-complex polarized sources, those objects whose frequency-dependent polarization behavior indicates the presence of material possessing complicated magnetoionic structure along the line of sight (LOS). For sources classified as Faraday-complex, we have analyzed a number of their radio and multiwavelength properties to determine whether they differ from Faraday-simple polarized sources (sources for which LOS magnetoionic structures are comparatively simple) in these properties. We use this information to constrain the physical nature of the magnetoionic structures responsible for generating the observed complexity. We detect Faraday complexity in 12% of polarized sources at ~1' resolution, but we demonstrate that underlying signal-to-noise limitations mean the true percentage is likely to be significantly higher in the polarized radio source population. We find that the properties of Faraday-complex objects are diverse, but that complexity is most often associated with depolarization of extended radio sources possessing a relatively steep total intensity spectrum. We find an association between Faraday complexity and LOS structure in the Galactic interstellar medium (ISM) and claim that a significant proportion of the Faraday complexity we observe may be generated at interfaces of the ISM associated with ionization fronts near neutral hydrogen structures. Galaxy cluster environments and internally generated Faraday complexity provide possible alternative explanations in some cases.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/187
- Title:
- Spot parameters on KIC solar-type stars
- Short Name:
- J/ApJ/871/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Active solar-type stars show large quasi-periodic brightness variations caused by stellar rotation with star spots, and the amplitude changes as the spots emerge and decay. The Kepler data are suitable for investigations of the emergence and decay processes of star spots, which are important to understand the underlying stellar dynamo and stellar flares. In this study, we measured the temporal evolution of the star-spot area with Kepler data by tracing the local minima of the light curves. In this analysis, we extracted the temporal evolution of star spots showing clear emergence and decay without being disturbed by stellar differential rotation. We applied this method to 5356 active solar-type stars observed by Kepler and obtained temporal evolution of 56 individual star spots. We calculated the lifetimes and emergence/decay rates of the star spots from the obtained temporal evolution of the spot area. As a result, we found that the lifetimes (T) of star spots range from 10 to 350days when the spot areas (A) are 0.1%-2.3% of the solar hemisphere. We also compared them with sunspot lifetimes and found that the lifetimes of star spots are much shorter than those extrapolated from an empirical relation of sunspots (T{propto}A), while being consistent with other research on star-spot lifetimes. The emergence and decay rates of star spots are typically 5x10^20^Mx/hr (8MSH/hr) with an area of 0.1%-2.3% of the solar hemisphere and mostly consistent with those expected from sunspots, which may indicate the same underlying processes.
- ID:
- ivo://CDS.VizieR/J/other/A+ARV/17.251
- Title:
- Stars observed with Doppler imaging
- Short Name:
- J/other/A+ARV/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere. This article is an attempt to review our current knowledge of starspots.
