## Recent Postings from Solar and Stellar

### New OB star candidates in the Carina Arm around Westerlund 2 from VPHAS+

O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrise OB star candidates in the Southern Galactic plane, down to a limiting magnitude of $g=20$. A 2 square-degree field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the $(u-g, g-r)$ diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ $u, g, r, i$ with published $J, H, K$ photometry in order to derive posterior probability distributions of the stellar parameters $\log(\rm T_{\rm eff})$ and distance modulus, together with the reddening parameters $A_0$ and $R_V$. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of $\sigma(A_0)\sim0.09$ and $\sigma(R_V)\sim0.08$. There are 489 objects that fit well as new OB candidates, earlier than $\sim$B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with $3.5<R_V<4$.

### Solar type II radio bursts associated with CME expansions as shown by EUV waves

We investigate the physical conditions of the sources of two metric Type-II bursts associated with CME expansions with the aim of verifying the relationship between the shocks and the CMEs, comparing the heights of the radio sources and the heights of the EUV waves associated with the CMEs. The heights of the EUV waves associated with the events were determined in relation to the wave fronts. The heights of the shocks were estimated by applying two different density models to the frequencies of the Type-II emissions and compared with the heights of the EUV waves. For the 13 June 2010 event, with band-splitting, the shock speed was estimated from the frequency drifts of the upper and lower branches of the harmonic lane, taking into account the H/F frequency ratio fH/fF = 2. Exponential fits on the intensity maxima of the branches revealed to be more consistent with the morphology of the spectrum of this event. For the 6 June 2012 event, with no band-splitting and with a clear fundamental lane on the spectrum, the shock speed was estimated directly from the frequency drift of the fundamental emission, determined by linear fit on the intensity maxima of the lane. For each event, the most appropriate density model was adopted to estimate the physical parameters of the radio source. The 13 June 2010 event presented a shock speed of 664-719 km/s, consistent with the average speed of the EUV wave fronts of 609 km/s. The 6 June 2012 event was related to a shock of speed of 211-461 km/s, also consistent with the average speed of the EUV wave fronts of 418 km/s. For both events, the heights of the EUV wave revealed to be compatible with the heights of the radio source, assuming a radial propagation of the shock.

### Time-variable non-thermal emission in the planetary nebula IRAS 15103-5754

The beginning of photoionization marks the transition between the post-Asymptotic Giant Branch (post-AGB) and planetary nebula (PN) phases of stars with masses < 8 M_sun. This critical phase is difficult to observe, as it lasts only a few decades. The combination of jets and magnetic fields, the key agents of PNe shaping, could give rise to synchrotron emission, but this has never been observed before in any PNe, since free-free emission from the ionized gas is expected to dominate its radio spectrum. In this paper we report radio continuum observations taken with the Australia Telescope Compact Array between 1 and 46 GHz of the young PN IRAS 15103-5754. Our observations in 2010-2011 show non-thermal emission compatible with synchrotron emission from electrons accelerated at a shock with spectral index $\alpha \simeq -0.54$. However, in 2012, the spectral index $\alpha \simeq -0.28$ is no longer compatible with synchrotron emission in these types of processes. Several hypothesis are discussed to explain this change. The more plausible ones are related to the presence of the newly photoionized region in this young PN: either energy loss of electrons due to Coulomb collisions with the plasma, or selective suppression of synchrotron radiation due to the Razin effect. We postulate that the observed flattening of non-thermal radio spectra could be a hallmark identifying the beginning of the PN phase.

### E-BOSS: An Extensive stellar BOw Shock Survey. II. Catalogue second release

Context. Stellar bow shocks have been studied not only observationally, but also theoretically since the late 1980s. Only a few catalogues of them exist. The bow shocks show emission along all the electromagnetic spectrum, but they are detected more easily in infrared wavelengths. The release of new and high-quality infrared data eases the discovery and subsequent study of new objects. Aims. We search stellar bow-shock candidates associated with nearby runaway stars, and gather them together with those found elsewhere, to enlarge the list of the E-BOSS first release. We aim to characterize the bow-shock candidates and provide a database suitable for statistical studies. We investigate the low-frequency radio emission at the position of the bow-shock features, that can contribute to further studies of high-energy emission from these objects. Methods. We considered samples from different literature sources and searched for bow-shaped structures associated with stars in the Wide-field Infrared Survey Explorer (WISE) images. We looked for each bow-shock candidate on centimeter radio surveys. Results. We reunited 45 bow-shock candidates and generated composed WISE images to show the emission in different infrared bands. Among them there are new sources, previously studied objects, and bow shocks found serendipitously. Five bow shocks show evidence of radio emission. Conclusions. Stellar bow shocks constitute an active field with open questions and enormous amounts of data to be analyzed. Future research at all wavelengths databases, and use of instruments like Gaia, will provide a more complete picture of these objects. For instance, infrared spectral energy distributions can give information about physical parameters of the bow shock matter. In addition, dedicated high-sensitivity radio observations can help to understand the radio-$\gamma$ connection.

### The IACOB spectroscopic database: recent updates and first data release

The IACOB project is an ambitious long-term project which is contributing to step forward in our knowledge about the physical properties and evolution of Galactic massive stars. The project aims at building a large database of high-resolution, multi-epoch, spectra of Galactic OB stars, and the scientific exploitation of the database using state-of-the-art models and techniques. In this proceeding, we summarize the latest updates of the IACOB spectroscopic database and highlight some of the first scientific results from the IACOB project; we also announce the first data release and the first public version of the iacob-broad tool for the line-broadening characterization of OB-type spectra.

### A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves

There are many Slowly Pulsating B (SPB) stars and gamma Dor stars in the Kepler Mission data set. The light curves of these pulsating stars have been classified phenomenologically into stars with symmetric light curves and with asymmetric light curves. In the same effective temperature ranges as the gamma Dor and SPB stars, there are variable stars with downward light curves that have been conjectured to be caused by spots. Among these phenomenological classes of stars, some show frequency groups’ in their amplitude spectra that have not previously been understood. While it has been recognised that nonlinear pulsation gives rise to combination frequencies in a Fourier description of the light curves of these stars, such combination frequencies have been considered to be a only a minor constituent of the amplitude spectra. In this paper we unify the Fourier description of the light curves of these groups of stars, showing that many of them can be understood in terms of only a few base frequencies, which we attribute to g mode pulsations, and combination frequencies, where sometimes a very large number of combination frequencies dominate the amplitude spectra. The frequency groups seen in these stars are thus tremendously simplified. We show observationally that the combination frequencies can have amplitudes greater than the base frequency amplitudes, and we show theoretically how this arises. Thus for some gamma Dor and SPB stars combination frequencies can have the highest observed amplitudes. Among the B stars are pulsating Be stars that show emission lines in their spectra from occasional ejection of material into a circumstellar disk. Our analysis gives strong support to the understanding of these pulsating Be stars as rapidly rotating SPB stars, explained entirely by g mode pulsations.

### Massive disk outflows mediated by extreme magnetic fields

We argue that magnetic fields amplified within a very high accretion-rate disk around main sequence stars can lead to the formation of massive bipolar outflows that can remove most of the disk’s mass and energy. This efficient directional removal of energy and mass allows the high accretion-rate disk to be built. We construct thick disks where the magnetic fields are amplified by an Alpha-Omega dynamo in the disk, bringing the fluctuating components of the magnetic field to be much stronger than the large-scale component. By examining the possible activity of the magnetic fields we conclude that main sequence stars can accrete mass at very high rates, up to 0.01Mo/yr for solar type stars, and up to 1Mo/yr for very massive stars. Such energetic outflows can account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, such as the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; Red Novae; Red Transients). Such powerful outflows can also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems where the companion is a main sequence star.

### Statistical studies of supernova environments

Investigations of the environments of SNe allow statistical constraints to be made on progenitor properties. We review progress that has been made in this field. Pixel statistics using tracers of e.g. star formation within galaxies show differences in the explosion sites of, in particular SNe types II and Ibc (SNe II and SNe Ibc), suggesting differences in population ages. Of particular interest is that SNe Ic are significantly more associated with H-alpha emission than SNe Ib, implying shorter lifetimes for the former. In addition, such studies have shown that the interacting SNe IIn do not explode in regions containing the most massive stars, which suggests that at least a significant fraction of their progenitors arise from the lower end of the core-collapse SN mass range. Host HII region spectroscopy has been obtained for a significant number of core-collapse events, however definitive conclusions have to-date been elusive. Single stellar evolution models predict that the fraction of SNe Ibc to SNe II should increase with increasing metallicity, due to the dependence of mass-loss rates on progenitor metallicity. We present a meta-analysis of host HII region oxygen abundances for CC SNe. It is concluded that the SN II to SN Ibc ratio shows little variation with oxygen abundance, with only a suggestion that the ratio increases in the lowest bin. Radial distributions of different SNe are discussed, where a central excess of SNe Ibc has been observed within disturbed galaxy systems, which is difficult to ascribe to metallicity or selection effects. Environment studies are evolving to enable studies at higher spatial resolutions than previously possible, while in addition the advent of wide-field integral field unit instruments allows galaxy-wide spectral analyses which will provide fruitful results to this field. Some example contemporary results are shown in that direction.

### Testing the recovery of stellar rotation signals from Kepler light curves using a blind hare-and-hounds exercise

We present the results of a blind exercise to test the recoverability of stellar rotation and differential rotation in Kepler light curves. The simulated light curves lasted 1000 days and included activity cycles, Sun-like butterfly patterns, differential rotation and spot evolution. The range of rotation periods, activity levels and spot lifetime were chosen to be representative of the Kepler data of solar like stars. Of the 1000 simulated light curves, 770 were injected into actual quiescent Kepler light curves to simulate Kepler noise. The test also included five 1000-day segments of the Sun’s total irradiance variations at different points in the Sun’s activity cycle. Five teams took part in the blind exercise, plus two teams who participated after the content of the light curves had been released. The methods used included Lomb-Scargle periodograms and variants thereof, auto-correlation function, and wavelet-based analyses, plus spot modelling to search for differential rotation. The results show that the overall’ period is well recovered for stars exhibiting low and moderate activity levels. Most teams reported values within 10% of the true value in 70% of the cases. There was, however, little correlation between the reported and simulated values of the differential rotation shear, suggesting that differential rotation studies based on full-disk light curves alone need to be treated with caution, at least for solar-type stars. The simulated light curves and associated parameters are available online for the community to test their own methods.

### Time variation of Kepler transits induced by stellar rotating spots - a way to distinguish between prograde and retrograde motion. II. Application to KOIs

Mazeh, Holczer, and Shporer (2015) have presented an approach that can, in principle, use the derived transit timing variation (TTV) of some transiting planets observed by the Kepler mission to distinguish between prograde and retrograde motion of their orbits with respect to the rotation of their parent stars. The approach utilizes TTVs induced by spot-crossing events that occur when the transiting planet moves across a spot on the stellar surface, by looking for a correlation between the derived TTVs and the stellar brightness derivatives at the corresponding transits, even in data that can not resolve the spot-crossing events themselves. We present here the application of this approach to the Kepler KOIs, identifying nine systems where the photometric spot modulation is large enough and the transit timing accurate enough to allow detection of a TTV-brightness-slope correlation. Excluding KOI-1546, which has been found recently to be a stellar binary, we are left with eight hot-Jupiter systems with high sensitivity to the correlation detection. Five of those eight systems show highly significant prograde motion, including two confirmed planets (KOI-203.01 = Kepler-17b and KOI-217.01 = Kepler-71b) and three planetary candidates (KOI-883.01, KOI-895.01, and KOI-1074.01), while no system displays retrograde motion, consistent with the suggestion that planets orbiting cool stars have prograde motion. All five systems have derived impact parameter $\lesssim$0.5, and all systems with an impact parameter in that range show significant correlation, except KOI-3.01 (= Kepler-3b = HAT-P-11b) where the lack of a correlation is explained by its large stellar obliquity. Although our sample is small, these findings hint that stellar spots, or at least the larger ones, have a tendency to be located at a low latitude on the stellar disc, similar to the Sun.

### Higgs portals to pulsar collapse [Cross-Listing]

Pulsars apparently missing from the galactic center could have been destroyed by asymmetric fermionic dark matter ($m_X = 1-100$ GeV) coupled to a light scalar ($m_{\phi}= 5-20$ MeV), which mixes with the Higgs boson. We point out that this pulsar-collapsing dark sector can resolve the core-cusp problem and will either be excluded or discovered by upcoming direct detection experiments. Another implication is a maximum pulsar age curve that increases with distance from the galactic center, with a normalization that depends on the couplings and masses of dark sector particles. In addition, we use old pulsars outside the galactic center to place bounds on asymmetric Higgs portal models.

### Higgs portals to pulsar collapse

Pulsars apparently missing from the galactic center could have been destroyed by asymmetric fermionic dark matter ($m_X = 1-100$ GeV) coupled to a light scalar ($m_{\phi}= 5-20$ MeV), which mixes with the Higgs boson. We point out that this pulsar-collapsing dark sector can resolve the core-cusp problem and will either be excluded or discovered by upcoming direct detection experiments. Another implication is a maximum pulsar age curve that increases with distance from the galactic center, with a normalization that depends on the couplings and masses of dark sector particles. In addition, we use old pulsars outside the galactic center to place bounds on asymmetric Higgs portal models.

### Thermal properties of hot and dense matter with finite range interactions

We explore the thermal properties of hot and dense matter using a model that reproduces the empirical properties of isospin symmetric and asymmetric bulk nuclear matter, optical model fits to nucleon-nucleus scattering data, heavy-ion flow data in the energy range 0.5-2 GeV/A, and the largest well-measured neutron star mass of 2 $\rm{M}_\odot$. Results of this model which incorporates finite range interactions through Yukawa type forces are contrasted with those of a zero-range Skyrme model that yields nearly identical zero-temperature properties at all densities for symmetric and asymmetric nucleonic matter and the maximum neutron star mass, but fails to account for heavy-ion flow data due to the lack of an appropriate momentum dependence in its mean field. Similarities and differences in the thermal state variables and the specific heats between the two models are highlighted. Checks of our exact numerical calculations are performed from formulas derived in the strongly degenerate and non-degenerate limits. Our studies of the thermal and adiabatic indices, and the speed of sound in hot and dense matter for conditions of relevance to core-collapse supernovae, the thermal evolution of neutron stars from their birth and mergers of compact binary stars reveal that substantial variations begin to occur at sub-saturation densities before asymptotic values are reached at supra-nuclear densities.

### The age-metallicity dependence for white dwarfs

We present a theoretical study on the metallicity dependence of the initial$-$to$-$final mass relation and its influence on white dwarf age determinations. We compute a grid of evolutionary sequences from the main sequence to $\sim 3\, 000$ K on the white dwarf cooling curve, passing through all intermediate stages. During the thermally-pulsing asymptotic giant branch no third dredge-up episodes are considered and thus the photospheric C/O ratio is below unity for sequences with metallicities larger than $Z=0.0001$. We consider initial metallicities from $Z=0.0001$ to $Z=0.04$, accounting for stellar populations in the galactic disk and halo, with initial masses below $\sim 3M_{\odot}$. We found a clear dependence of the shape of the initial$-$to$-$final mass relation with the progenitor metallicity, where metal rich progenitors result in less massive white dwarf remnants, due to an enhancement of the mass loss rates associated to high metallicity values. By comparing our theoretical computations with semi empirical data from globular and old open clusters, we found that the observed intrinsic mass spread can be accounted for by a set of initial$-$to$-$final mass relations characterized by different metallicity values. Also, we confirm that the lifetime spent before the white dwarf stage increases with metallicity. Finally, we estimate the mean mass at the top of the white dwarf cooling curve for three globular clusters NGC 6397, M4 and 47 Tuc, around $0.53 M_{\odot}$, characteristic of old stellar populations. However, we found different values for the progenitor mass, lower for the metal poor cluster, NGC 6397, and larger for the younger and metal rich cluster 47 Tuc, as expected from the metallicity dependence of the initial$-$to$-$final mass relation.

### Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA

Transitional disks with large dust cavities are important laboratories to study planet formation and disk evolution. Cold gas may still be present inside these cavities, but the quantification of this gas is challenging. The gas content is important to constrain the origin of the dust cavity. We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of 12CO 6–5 and 690 GHz (Band 9) continuum of five well-studied transitional disks. In addition, we analyze previously published Band 7 observations of a disk in 12CO 3–2 line and 345 GHz continuum. The observations are used to set constraints on the gas and dust surface density profiles, in particular the drop delta-gas of the gas density inside the dust cavity. The physical-chemical modeling code DALI is used to analyze the gas and dust images simultaneously. We model SR21, HD135344B, LkCa15, SR24S and RXJ1615-3255 (Band 9) and J1604-2130 (Band 7). The SED and continuum visibility curve constrain the dust surface density. Subsequently, the same model is used to calculate the 12CO emission, which is compared with the observations through spectra and intensity cuts. The amount of gas inside the cavity is quantified by varying the delta-gas parameter. Model fits to the dust and gas indicate that gas is still present inside the dust cavity for all disks but at a reduced level. The gas surface density drops inside the cavity by at least a factor 10, whereas the dust density drops by at least a factor 1000. Disk masses are comparable with previous estimates from the literature, cavity radii are found to be smaller than in the 345 GHz SubMillimeter Array (SMA) data. The derived gas surface density profiles suggest clearing of the cavity by one or more companions in all cases, trapping the millimeter-sized dust at the edge of the cavity.

### New age-metallicity diagnostic diagram for the Washington photometric system

The age calibration of the Washington deltaT1 index is mainly used to estimate ages of star clusters older than 1 Gyr, no age-metallicity degeneracy effect is considered. We have profusely exploited synthetic T1 versus C-T1 colour magnitude diagrams aiming at exploring the intrinsic behaviour of the deltaT1 index. The analysis shows that deltaT1 varies with age and metal content as well. In general, the dependence on age weakens for ages greater than ~ 6 Gyr, and results even less sensitive to age as the metallicity decreases. For ages younger than ~ 5 Gyr deltaT1 shows a strong correlation with both age and metallicity. The deltaC index -defined as deltaT1 for the C passband- is also a combined measurement of age and metallicity. We introduce a new age-metallicity diagnostic diagram, deltaT1 versus deltaC – deltaT1, which has shown the ability of unambiguously providing age and metallicity estimates, simultaneously. The new procedure allows to derive ages from 1 up to 13 Gyr and metallicities [Fe/H] from -2.0 up to +0.5 dex, and is independent of the cluster reddening and distance modulus. It does solve the constraints found in the deltaT1 index and surpasses the performance of the standard giant branch metallicity method. All these features make the diagnostic diagram a powerful tool for estimating accurate ages as well as metallicities.

### New variables in M5 (NGC 5904) and some identification corrections

We report twelve variables not previously detected in the globular cluster M5 (NGC 5904); one SX Phe and eleven semi-regular variables (SR). Their identifications, equatorial coordinates, ephemerides, and light curves are given. Furthermore, we have explored the light curves of a group of stars whose variability has not been confirmed and that are marked as probable non- variables in the CVSGC. Finally, we offer detailed identifications for some of the known variables in crowded regions that were misidentified in previous studies. We shall also address the cases of the cataclysmic variable or U Gem type V101 and of the variable blue straggler V159.

### The Physical Nature and Orbital Behavior of the Eclipsing System DK Cygni [Replacement]

New CCD photometry is presented for the hot overcontact binary DK Cyg, together with reasonable explanations for the light and period variations. Historical light and velocity curves from 1962 to 2012 were simultaneously analyzed with the Wilson-Devinney (W-D) synthesis code. The brightness disturbances were satisfactorily modeled by applying a magnetic cool spot on the primary star. Based on 261 times of minimum light including 116 new timings and spanning more than 87 yrs, a period study reveals that the orbital period has varied due to a periodic oscillation superposed on an upward parabola. The period and semi-amplitude of the modulation are about 78.1 yrs and 0.0037 d, respectively. This detail is interpreted as a light-travel-time effect due to a circumbinary companion with a minimum mass of $M_3$=0.065 $M_\odot$, within the theoretical limit of $\sim$0.07 M$_\odot$ for a brown dwarf star. The observed period increase at a fractional rate of $+$2.74 $\times$10$^{-10}$ is in excellent agreement with that calculated from our W-D synthesis. Mass transfer from the secondary to the primary component is mainly responsible for the secular period change. We examined the evolutionary status of the DK Cyg system from the absolute dimensions.

### Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions

We present a new method for performing differential emission measure (DEM) inversions on narrow-band EUV images from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The method yields positive definite DEM solutions by solving a linear program. This method has been validated against a diverse set of thermal models of varying complexity and realism. These include (1) idealized gaussian DEM distributions, (2) 3D models of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a non-linear force-free field, and (3) thermodynamic models from a fully-compressible, 3D MHD simulation of AR corona formation following magnetic flux emergence. We then present results from the application of the method to AIA observations of Active Region 11158, comparing the region’s thermal structure on two successive solar rotations. Additionally, we show how the DEM inversion method can be adapted to simultaneously invert AIA and XRT data, and how supplementing AIA data with the latter improves the inversion result. The speed of the method allows for routine production of DEM maps, thus facilitating science studies that require tracking of the thermal structure of the solar corona in time and space.

### Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856

Recent studies have shown that the extended main-sequence turn off (eMSTO) is a common feature of intermediate-age star clusters in the Magellanic Clouds (MCs). The most simple explanation is that these stellar systems harbor multiple generations of stars with an age difference of a few hundred Myrs. However, while an eMSTO has been detected in a large number of clusters with ages between ~1-2 Gyrs, several studies of young clusters in both MCs and in nearby galaxies do not find any evidence for a prolonged star-formation history, i.e. for multiple stellar generations. These results have suggested alternative interpretation of the eMSTOs observed in intermediate-age star clusters. The eMSTO could be due to stellar rotation mimicking an age spread or to interacting binaries. In these scenarios, intermediate-age MC clusters would be simple stellar populations, in close analogy with younger clusters. Here we provide the first evidence for an eMSTO in a young stellar cluster. We exploit multi-band Hubble Space Telescope photometry to study the ~300-Myr old star cluster NGC1856 in the Large Magellanic Cloud and detected a broadened MSTO that is consistent with a prolonged star-formation which had a duration of about 150 Myrs. Below the turn-off, the MS of NGC1856 is split into a red and blue component, hosting 33+/-5% and 67+/-5% of the total number of MS stars, respectively. We discuss these findings in the context of multiple-stellar-generation, stellar-rotation, and interacting-binary hypotheses.

### New binaries among UV-selected, hot subdwarf stars and population properties

We have measured the orbital parameters of seven close binaries, including six new objects, in a radial velocity survey of 38 objects comprising a hot subdwarf star with orbital periods ranging from ~0.17 to 3 d. One new system, GALEX J2205-3141, shows reflection on a M dwarf companion. Three other objects show significant short-period variations, but their orbital parameters could not be constrained. Two systems comprising a hot subdwarf paired with a bright main-sequence/giant companion display short-period photometric variations possibly due to irradiation or stellar activity and are also short-period candidates. All except two candidates were drawn from a selection of subluminous stars in the Galaxy Evolution Explorer ultraviolet sky survey. Our new identifications also include a low-mass subdwarf B star and likely progenitor of a low mass white dwarf (GALEX J0805-1058) paired with an unseen, possibly substellar, companion. The mass functions of the newly identified binaries imply minimum secondary masses ranging from 0.03 to 0.39 M_solar. Photometric time series suggest that, apart from GALEX J0805-1058 and J2205-3141, the companions are most likely white dwarfs. We update the binary population statistics: Close to 40 per cent of hot subdwarfs have a companion. Also, we found that the secondary mass distribution shows a low-mass peak attributed to late-type dwarfs, and a higher-mass peak and tail distribution attributed to white dwarfs and a few spectroscopic composites. Also, we found that the population kinematics imply an old age and include a few likely halo population members.

### The Herschel view of the nebula around the luminous blue variable star AG Carinae

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter. In the infrared light, the nebula appears as a clumpy ring shell that extends up to 1.2 pc with an inner radius of 0.4 pc. It coincides with the Halpha nebula, but extends further out. Dust modeling of the nebula was performed and indicates the presence of large grains. The dust mass is estimated to be ~ 0.2 Msun. The infrared spectrum of the nebula consists of forbidden emission lines over a dust continuum. Apart from ionized gas, these lines also indicate the existence of neutral gas in a photodissociation region that surrounds the ionized region. The abundance ratios point towards enrichment by processed material. The total mass of the nebula ejected from the central star amounts to ~ 15 Msun, assuming a dust-to-gas ratio typical of LBVs. The abundances and the mass-loss rate were used to constrain the evolutionary path of the central star and the epoch at which the nebula was ejected, with the help of available evolutionary models. This suggests an ejection during a cool LBV phase for a star of ~ 55 Msun with little rotation.

### Stellar mixing length theory with entropy rain

Stellar mixing length theory is modified to include the effects of a nongradient term that originates from the motion of convective elements with entropy perturbations of either sign. It is argued that such a term, first studied by Deardorff in the meteorological context, represents the effects of thin intense downdrafts caused by the rapid cooling in the granulation layer at the top of the convection zone. They transport heat nonlocally, as originally anticipated by Spruit in the 1990s, who describes the convection in the strongly stratified simulations of Stein & Nordlund as entropy rain. Although our model has ill-determined free parameters, it demonstrates that solutions can be found that look similar to the original ones, except that the deeper layers are now Schwarzschild stable, so no giant cells are produced and the typical convective scale is that of granules even at larger depth. Consequences for modeling solar differential, the global dynamo, and sunspots are briefly discussed.

### Flare Hybrids

Svestka (Solar Phys. 1989, 121, 399) on the basis of the Solar Maximum Mission observations introduced a new class of flares, the so-called flare hybrids. When they start, they look as typical compact flares (phase 1), but later on they look like flares with arcades of magnetic loops (phase 2). We summarize the features of flare hybrids in soft and hard X-rays as well as in extreme-ultraviolet; these allow us to distinguish them from other flares. Additional energy release or long plasma cooling timescales have been suggested as possible cause of phase 2. Estimations of frequency of flare hybrids have been given. Magnetic configurations supporting their origin have been presented. In our opinion, flare hybrids are quite frequent and a difference between lengths of two interacting systems of magnetic loops is a crucial parameter for recognizing their features.