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- ID:
- ivo://CDS.VizieR/J/A+A/446/773
- Title:
- GLMP sample of galactic OH/IR stars
- Short Name:
- J/A+A/446/773
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical and near-infrared finding charts taken from the DSS and 2MASS surveys of 94 IRAS sources selected from the GLMP catalogue, and accurate astrometry (~0.2") for most of them. Selection criteria were very red IRAS colours representative for OH/IR stars with optically thick circumstellar shells and the presence of variability according to the IRAS variability index (VAR>50). The main photometric properties of the stars in this `GLMP sample' are presented, discussed and compared with the correspondent properties of the `Arecibo sample' of OH/IR stars studied nearlier. We find that 37% of the sample (N=34) has no counterpart in the 2MASS, implying extremely high optical depths of their shells. Most of the sources identified in the 2MASS are faint (K>~8) and are of very red colour in the near-infrared, as expected. The brightest 2MASS counterpart (K=5.3mag) was found for IRAS18299-1705. Its blue colour H-K=1.3 suggests that IRAS18299-1705 is a post-AGB star. Few GLMP sources have faint but relatively blue counterparts. They might be misidentified field stars or stars that recently experienced a drop of their mass loss rates. The `GLMP sample' in general is made of oxygen-rich AGB stars, which are highly obscured by their circumstellar shells. They belong to the same population as the reddest OH/IR stars in the `Arecibo sample'.
- ID:
- ivo://CDS.VizieR/J/ApJ/797/50
- Title:
- Global energetics of solar flares. I.
- Short Name:
- J/ApJ/797/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first part of a project on the global energetics of solar flares and coronal mass ejections that includes about 400 M- and X-class flares observed with Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). We calculate the potential (E_p_), the nonpotential (E_np_) or free energies (E_free_=E_np_-E_p_), and the flare-dissipated magnetic energies (E_diss_). We calculate these magnetic parameters using two different NLFFF codes: the COR-NLFFF code uses the line-of-sight magnetic field component B_z_ from HMI to define the potential field, and the two-dimensional (2D) coordinates of automatically detected coronal loops in six coronal wavelengths from AIA to measure the helical twist of coronal loops caused by vertical currents, while the PHOT-NLFFF code extrapolates the photospheric three-dimensional (3D) vector fields. We find agreement between the two codes in the measurement of free energies and dissipated energies within a factor of <~3. The size distributions of magnetic parameters exhibit powerlaw slopes that are approximately consistent with the fractal-diffusive self-organized criticality model. The magnetic parameters exhibit scaling laws for the nonpotential energy, E_np_{propto}E_p_^1.02^, for the free energy, E_free_{propto}E_p_^1.7^ and E_free_{propto}B_{phi}_^1.0^L^1.5^, for the dissipated energy, E_diss_{propto}E_p_^1.6^ and E_diss_{propto}E_free_^0.9^ , and the energy dissipation volume, V{propto}E_diss_^1.2^. The potential energies vary in the range of E_p_=1x10^31^-4x10^33^erg, while the free energy has a ratio of E_free_/E_p_{approx}1%-25%. The Poynting flux amounts to F_flare_{approx}5x10^8^-10^10^erg/cm2/s during flares, which averages to F_AR_{approx}6x10^6^erg/cm2/s during the entire observation period and is comparable with the coronal heating rate requirement in active regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/802/53
- Title:
- Global energetics of solar flares. II.
- Short Name:
- J/ApJ/802/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the second part of a project on the global energetics of solar flares and coronal mass ejections that includes about 400 M- and X-class flares observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during the first 3.5yr of its mission. In this Paper II we compute the differential emission measure (DEM) distribution functions and associated multithermal energies, using a spatially-synthesized Gaussian DEM forward-fitting method. The multithermal DEM function yields a significantly higher (by an average factor of ~14), but more comprehensive (multi-) thermal energy than an isothermal energy estimate from the same AIA data. We find a statistical energy ratio of E_th_/E_diss_~2-40% between the multithermal energy E_th_ and the magnetically dissipated energy E_diss_, which is an order of magnitude higher than the estimates of Emslie et al. (2012ApJ...759...71E). For the analyzed set of M- and X-class flares we find the following physical parameter ranges: L=10^8.2^-10^9.7^cm for the length scale of the flare areas, T_p_=10^5.7^-10^7.4^K for the DEM peak temperature, T_w_=10^6.8^-10^7.6^K for the emission measure-weighted temperature, n_p_=10^10.3^-10^11.8^/cm3 for the average electron density, EM_p_=10^47.3^-10^50.3^/cm3 for the DEM peak emission measure, and E_th_=10^26.8^-10^32.0^erg for the multithermal energies. The deduced multithermal energies are consistent with the RTV scaling law E_th,RTV_=73x10^-10^T_p_^3^L_p_^2^, which predicts extremal values of E_th,max_~1.5x10^33^erg for the largest flare and E_th,min_~1x10^24^erg for the smallest coronal nanoflare. The size distributions of the spatial parameters exhibit powerlaw tails that are consistent with the predictions of the fractal-diffusive self-organized criticality model combined with the RTV scaling law.
- ID:
- ivo://CDS.VizieR/J/ApJ/832/27
- Title:
- Global energetics of solar flares. III.
- Short Name:
- J/ApJ/832/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study entails the third part of a global flare energetics project, in which Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data of 191 M and X-class flare events from the first 3.5yrs of the Solar Dynamics Observatory mission are analyzed. We fit a thermal and a nonthermal component to RHESSI spectra, yielding the temperature of the differential emission measure (DEM) tail, the nonthermal power-law slope and flux, and the thermal/nonthermal cross-over energy e_co_. From these parameters, we calculate the total nonthermal energy E_nt_ in electrons with two different methods: (1) using the observed cross-over energy e_co_ as low-energy cutoff, and (2) using the low-energy cutoff e_wt_ predicted by the warm thick-target bremsstrahlung model of Kontar et al. Based on a mean temperature of T_e_=8.6MK in active regions, we find low-energy cutoff energies of e_wt_=6.2+/-1.6keV for the warm-target model, which is significantly lower than the cross-over energies e_co_=21+/-6keV. Comparing with the statistics of magnetically dissipated energies E_mag_ and thermal energies E_th_ from the two previous studies, we find the following mean (logarithmic) energy ratios with the warm-target model: E_nt_=0.41E_mag_, E_th_=0.08E_mag_, and E_th_=0.15E_nt_. The total dissipated magnetic energy exceeds the thermal energy in 95% and the nonthermal energy in 71% of the flare events, which confirms that magnetic reconnection processes are sufficient to explain flare energies. The nonthermal energy exceeds the thermal energy in 85% of the events, which largely confirms the warm thick-target model.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/105
- Title:
- Global energetics of solar flares. IV. CME
- Short Name:
- J/ApJ/831/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study entails the fourth part of a global flare energetics project, in which the mass m_cme_, kinetic energy E_kin_, and the gravitational potential energy E_grav_ of coronal mass ejections (CMEs) is measured in 399 M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission, using a new method based on the extreme ultraviolet (EUV) dimming effect. EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV dimming method is truly complementary to the Thomson scattering method in white light, which probes the CME evolution in the heliosphere at r>~2R_{sun}_, while the EUV dimming method tracks the CME launch in the corona. We compare the CME parameters obtained in white light with the LASCO/C2 coronagraph with those obtained from EUV dimming with the Atmospheric Imaging Assembly onboard the SDO for all identical events in both data sets. We investigate correlations between CME parameters, the relative timing with flare parameters, frequency occurrence distributions, and the energy partition between magnetic, thermal, nonthermal, and CME energies. CME energies are found to be systematically lower than the dissipated magnetic energies, which is consistent with a magnetic origin of CMEs.
- ID:
- ivo://CDS.VizieR/J/ApJ/885/49
- Title:
- Global energetics of solar flares. IX.
- Short Name:
- J/ApJ/885/49
- Date:
- 08 Dec 2021
- Publisher:
- CDS
- Description:
- A more accurate analytical solution of the vertical-current approximation nonlinear force-free field (VCA3-NLFFF) model is presented that includes, besides the radial (Br) and azimuthal (B{phi}) magnetic field components, a poloidal component (B_{theta}_/=0) as well. This new analytical solution is of second-order accuracy in the divergence-freeness condition and of third-order accuracy in the force-freeness condition. We reanalyze the sample of 173 GOES M- and X-class flares observed with the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO). The new code reproduces helically twisted loops with a low winding number below the kink instability consistently, avoiding unstable, highly twisted structures of the Gold-Hoyle flux rope type. The magnetic energies agree within E_VCA3_/E_W_=0.99{+/-}0.21 with the Wiegelmann (W-NLFFF) code. The time evolution of the magnetic field reveals multiple, intermittent energy buildup and releases in most flares, contradicting both the Rosner-Vaiana model (with gradual energy storage in the corona) and the principle of timescale separation ({tau}flare<<{tau}storage) postulated in self-organized criticality models. The mean dissipated flare energy is found to amount to 7%{+/-}3% of the potential energy, or 60%{+/-}26% of the free energy, a result that can be used for predicting flare magnitudes based on the potential field of active regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/881/1
- Title:
- Global energetics of solar flares. VIII.
- Short Name:
- J/ApJ/881/1
- Date:
- 10 Dec 2021
- Publisher:
- CDS
- Description:
- One of the key problems in solar flare physics is the determination of the low-energy cut-off: the value that determines the energy of nonthermal electrons and hence flare energetics. We discuss different approaches to determine the low-energy cut-off in the spectrum of accelerated electrons: (I) the total electron number model, (II) the time-of-flight model (based on the equivalence of the time-of-flight and the collisional deflection time), (III) the warm target model of Kontar et al., and (IV) the model of the spectral cross-over between thermal and nonthermal components. We find that the first three models are consistent with a low-energy cutoff with a mean value of ~10keV, while the cross-over model provides an upper limit for the low-energy cutoff with a mean value of ~21keV. Combining the first three models we find that the ratio of the nonthermal energy to the dissipated magnetic energy in solar flares has a mean value of qE=0.57{+/-}0.08, which is consistent with an earlier study based on the simplified approximation of the warm target model alone (qE=0.51{+/-}0.17). This study corroborates the self-consistency between three different low-energy cutoff models in the calculation of nonthermal flare energies.
- ID:
- ivo://CDS.VizieR/J/AJ/136/159
- Title:
- Global 86GHz VLBI survey of compact radio sources
- Short Name:
- J/AJ/136/159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a large 86GHz global very long baseline interferometry (VLBI) survey of compact radio sources. The main goal of the survey is to increase by factors of 3-5 the total number of objects accessible for future 3mm VLBI imaging. The survey observations reach a baseline sensitivity of 0.1Jy and an image sensitivity of better than 10mJy/beam. A total of 127 compact radio sources have been observed. The observations have yielded images for 109 sources, extending the database of the sources imaged at 86GHz with VLBI observation by a factor of 5, and only six sources have not been detected. The remaining 12 objects have been detected but could not be imaged due to insufficient closure phase information.
- ID:
- ivo://CDS.VizieR/J/A+A/580/A43
- Title:
- Global HI content from a stacking experiment
- Short Name:
- J/A+A/580/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the atomic neutral hydrogen (HI) content of ~1600 galaxies up to z~0.1 using stacking techniques. The observations were carried out with the Westerbork Synthesis Radio Telescope (WSRT) in the area of the SDSS South Galactic Cap (SSGC), where we selected a galaxy sample from the SDSS spectroscopic catalog. Multi-wavelength information is provided by SDSS, NVSS, GALEX, and WISE. We use the collected information to study HI trends with color, star-forming, and active galactic nuclei (AGN) properties. Using near-UV (NUV)-r colors, galaxies are divided into blue cloud, green valley and red sequence galaxies.