The Early Phases of Supernova 2020pni: Shock-Ionization of the Nitrogen-Enriched Circumstellar Material

We present multiwavelength observations of the Type II SN 2020pni. Classified at $sim 1.3$ days after explosion, the object showed narrow (FWHM $<250,textrm{km},textrm{s}^{-1}$) recombination lines of ionized helium, nitrogen, and carbon, as typically seen in flash-spectroscopy events. Using the non-LTE radiative transfer code CMFGEN to model our first high resolution spectrum, we infer a progenitor mass-loss rate of $dot{M}=(3.5-5.3)times10^{-3}$ M$_{odot}$ yr$^{-1}$ (assuming a wind velocity of $v_w=200,textrm{km},textrm{s}^{-1}$), estimated at a radius of $R_{rm in}=2.5times10^{14},rm{cm}$. In addition, we find that the progenitor of SN 2020pni was enriched in helium and nitrogen (relative abundances in mass fractions of 0.30$-$0.40, and $8.2times10^{-3}$, respectively). Radio upper limits are also consistent with a dense CSM, and a mass-loss rate of $dot M>5 times 10^{-4},rm{M_{odot},yr^{-1}}$. During the first 4 days after first light, we also observe an increase in velocity of the hydrogen lines (from $sim 250,textrm{km},textrm{s}^{-1}$ to $sim 1000,textrm{km},textrm{s}^{-1}$), which suggests a complex CSM. The presence of dense and confined CSM, as well as its inhomogeneous structure, suggest a phase of enhanced mass loss of the progenitor of SN 2020pni during the last year before explosion. Finally, we compare SN 2020pni to a sample of other shock-photoionization events. We find no evidence of correlations among the physical parameters of the explosions and the characteristics of the CSM surrounding the progenitors of these events. This favors the idea that the mass-loss experienced by massive stars during their final years could be governed by stochastic phenomena, and that, at the same time, the physical mechanisms responsible for this mass-loss must be common to a variety of different progenitors.

The early discovery of SN 2017ahn: signatures of persistent interaction in a fast declining Type II supernova

We present high-cadence, comprehensive data on the nearby ($Dsimeq33,rm{Mpc}$) Type II SN 2017ahn, discovered within $sim$1 day of explosion, from the very early phases after explosion to the nebular phase. The observables of SN 2017ahn show a significant evolution over the $simeq470,rm{d}$ of our follow-up campaign, first showing prominent, narrow Balmer lines and other high-ionization features purely in emission (i.e. flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical Type II supernovae. Over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining H-rich core-collapse supernovae. The modeling of the light curves and early flash spectra suggest a complex circumstellar medium surrounding the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution being swept up by the rapidly expanding ejecta within the first $sim6,rm{d}$ of the supernova evolution, while signatures of interaction are observed also at later phases. Hydrodynamical models support the scenario in which linearly declining Type II supernovae are predicted to arise from massive yellow super/hyper giants depleted of most of their hydrogen layers.

Can we detect aurora in exoplanets orbiting M dwarfs?

New instruments and telescopes, such as SPIRou, CARMENES and TESS, will increase manyfold the number of known planets orbiting M dwarfs. To guide future radio observations, we estimate radio emission from known M-dwarf planets using the empirical radiometric prescription derived in the solar system, in which radio emission is powered by the wind of the host star. Using solar-like wind models, we find that the most promising exoplanets for radio detections are GJ 674 b and Proxima b, followed by YZ Cet b, GJ 1214 b, GJ 436 b. These are the systems that are the closest to us (<10 pc). However, we also show that our radio fluxes are very sensitive to the unknown properties of winds of M dwarfs. So, which types of winds would generate detectable radio emission? In a reverse engineering calculation, we show that winds with mass-loss rates dot{M} > kappa_sw /u_sw^3 would drive planetary radio emission detectable with present-day instruments, where u_{sw} is the local stellar wind velocity and kappa_sw is a constant that depends on the size of the planet, distance and orbital radius. Using observationally-constrained properties of the quiescent winds of GJ 436 and Proxima Cen, we conclude that it is unlikely that GJ 436 b and Proxima b would be detectable with present-day radio instruments, unless the host stars generate episodic coronal mass ejections. GJ 674 b, GJ 876 b and YZ Cet b could present good prospects for radio detection, provided that their host-stars winds have dot{M} u_sw^3 > 1.8e-4 Msun/yr (km/s)^3.

The diversity of supernovae and impostors shortly after explosion

Observational surveys are now able to detect an increasing number of transients, such as core-collapse supernovae (SN) and powerful non-terminal outbursts (SN impostors). Dedicated spectroscopic facilities can follow up these events shortly after detection. Here we investigate the properties of these explosions at early times. We use the radiative transfer code CMFGEN to build an extensive library of spectra simulating the interaction of supernovae and their progenitors winds/circumstellar medium (CSM). We consider a range of progenitor mass-loss rates (Mdot = 5e-4 to 1e-2 Msun/yr), abundances (solar, CNO-processed, and He-rich), and SN luminosities (L = 1.9e8 to 2.5e10 Lsun). The models simulate events ~1 day after explosion, and we assume a fixed location of the shock front as Rin=8.6e13 cm. We show that the large range of massive star properties at the pre-SN stage causes a diversity of early-time interacting SN and impostors. We identify three main classes of early-time spectra consisting of relatively high-ionisation (e.g. Ovi), medium-ionisation (e.g. Ciii), and low-ionisation lines (e.g. Feii/iii). They are regulated by L and the CSM density. Given a progenitor wind velocity Vinf, our models also place a lower limit of Mdot > 5e-4 (Vinf/150 km/s) Msun/yr for detection of CSM interaction signatures in observed spectra. Early-time SN spectra should provide clear constraints on progenitors by measuring H, He, and CNO abundances if the progenitors come from single stars. The connections are less clear considering the effects of binary evolution. Yet, our models provide a clear path for linking the final stages of massive stars to their post-explosion spectra at early times, and guiding future observational follow-up of transients with facilities such as the Zwicky Transient Facility.

Modelling the asymmetric wind of the luminous blue variable binary MWC 314

We present a spectroscopic analysis of MWC 314, a luminous blue variable (LBV) candidate with an extended bipolar nebula. The detailed spectroscopic variability is investigated to determine if MWC 314 is a massive binary system with a supersonically accelerating wind or a low-mass B[e] star. We compare the spectrum and spectral energy distribution to other LBVs (such as P Cyg) and find very similar physical wind properties, indicating strong kinship. We combined long-term high-resolution optical spectroscopic monitoring and V-band photometric observations to determine the orbital elements and stellar parameters and to investigate the spectral variability with the orbital phases. We developed an advanced model of the large-scale wind-velocity and wind-density structure with 3-D radiative transfer calculations that fit the orbitally modulated P Cyg profile of He I lam5876, showing outflow velocities above 1000 km/s. We find that MWC 314 is a massive semi-detached binary system of ~1.22 AU, observed at an inclination angle of i=72.8 deg. with an orbital period of 60.8 d and e=0.23. The primary star is a low-vsini LBV candidate of m1=39.6 Msun and R1=86.8 Rsun. The detailed radiative transfer fits show that the geometry of wind density is asymmetric around the primary star with increased wind density by a factor of 3.3, which leads the orbit of the primary. The variable orientation causes the orbital modulation that is observed in absorption portions of P Cyg wind lines. Wind accretion in the system produces a circumbinary disc. MWC 314 is in a crucial evolutionary phase of close binary systems, when the massive primary star has its H envelope being stripped and is losing mass to a circumbinary disc. MWC 314 is a key system for studying the evolutionary consequences of these effects.

Long-term Spectroscopic Monitoring of LBVs and LBV Candidates

We present results of a long-term spectroscopic monitoring program (since mid 2009) of Luminous Blue Variables with the new HERMES echelle spectrograph on the 1.2 m Mercator telescope at La Palma (Spain). We investigate high-resolution (R=80,000) optical spectra of two LBVs, P Cyg and HD 168607, the LBV candidates MWC 930 and HD 168625, and the LBV binary MWC 314. In P Cyg we observe flux changes in the violet wings of the Balmer H{alpha}, H{beta}, and He I lines between May and Sep 2009. The changes around 200 km/s to 300 km/s are caused by variable opacity at the base of the supersonic wind from the blue supergiant. We observe in MWC 314 broad double-peaked metal emission lines with invariable radial velocities over time. On the other hand, we measure in the photospheric S II {lambda}5647 absorption line, with lower excitation energy of ~14 eV, an increase of the heliocentric radial velocity centroid from 37 km/s to 70 km/s between 5 and 10 Sep 2009 (and 43 km/s on 6 Apr 2010). The increase of radial velocity of ~33 km/s in only 5 days can confirm the binary nature of this LBV close to the Eddington luminosity limit. A comparison with VLT-UVES and Keck-Hires spectra observed over the past 13 years reveals strong flux variability in the violet wing of the H{alpha} emission line of HD 168625, and in the absorption portion of the H{beta} line of HD 168607. In HD 168625 we observe H{alpha} wind absorption at velocities exceeding 200 km/s which develops between Apr and June 2010.

Resolving the asymmetric inner wind region of the yellow hypergiant IRC+10420 with VLTI/AMBER in low and high spectral resolution mode

We obtained near-infrared long-baseline interferometry of IRC+10420 with the AMBER instrument of ESOs Very Large Telescope Interferometer (VLTI) in low and high spectral resolution (HR) mode to probe the photosphere and the innermost circumstellar environment of this rapidly evolving yellow hypergiant. In the HR observations, the visibilities show a noticeable drop across the Brackett gamma (BrG) line on all three baselines, and we found differential phases up to -25 degrees in the redshifted part of the BrG line and a non-zero closure phase close to the line center. The calibrated visibilities were corrected for AMBERs limited field-of-view to appropriately account for the flux contribution of IRC+10420s extended dust shell. We derived FWHM Gaussian sizes of 1.05 +/- 0.07 and 0.98 +/- 0.10 mas for IRC+10420s continuum-emitting region in the H and K bands, respectively, and the BrG-emitting region can be fitted with a geometric ring model with a diameter of 4.18 +0.19/-0.09 mas, which is approximately 4 times the stellar size. The geometric model also provides some evidence that the BrG line-emitting region is elongated towards a position angle of 36 degrees, well aligned with the symmetry axis of the outer reflection nebula. The HR observations were further analyzed by means of radiative transfer modeling using CMFGEN and the 2-D Busche & Hillier codes. Our spherical CMFGEN model poorly reproduces the observed line shape, blueshift, and extension, definitively showing that the IRC+10420 outflow is asymmetric. Our 2-D radiative transfer modeling shows that the blueshifted BrG emission and the shape of the visibility across the emission line can be explained with an asymmetric bipolar outflow with a high density contrast from pole to equator (8-16), where the redshifted light is substantially diminished.

The qWR star HD 45166. II. Fundamental stellar parameters and evidence of a latitude-dependent wind

The enigmatic object HD 45166 is a qWR star in a binary system with an orbital period of 1.596 day, and presents a rich emission-line spectrum in addition to absorption lines from the companion star (B7 V). As the system inclination is very small (i=0.77 +- 0.09 deg), HD 45166 is an ideal laboratory for wind-structure studies. The goal of the present paper is to determine the fundamental stellar and wind parameters of the qWR star. A radiative transfer model for the wind and photosphere of the qWR star was calculated using the non-LTE code CMFGEN. The wind asymmetry was also analyzed using a recently-developed version of CMFGEN to compute the emerging spectrum in two-dimensional geometry. The temporal-variance spectrum (TVS) was calculated for studying the line-profile variations. Abundances, stellar and wind parameters of the qWR star were obtained. The qWR star has an effective temperature of Teff=50000 +- 2000 K, a luminosity of log(L/Lsun)=3.75 +- 0.08, and a corresponding photospheric radius of Rphot=1.00 Rsun. The star is helium-rich (N(H)/N(He) = 2.0), while the CNO abundances are anomalous when compared either to solar values, to planetary nebulae, or to WR stars. The mass-loss rate is Mdot = 2.2 . 10^{-7} Msun/yr, and the wind terminal velocity is vinf=425 km/s. The comparison between the observed line profiles and models computed under different latitude-dependent wind densities strongly suggests the presence of an oblate wind density enhancement, with a density contrast of at least 8:1 from equator to pole. If a high velocity polar wind is present (~1200 km/s), the minimum density contrast is reduced to 4:1. The wind parameters determined are unusual when compared to O-type stars or to typical WR stars. (abridged)

Detection of additional Wolf-Rayet stars in the starburst cluster Westerlund 1 with SOAR

We report the detection of 3 additional Wolf-Rayet stars in the young cluster Westerlund 1. They were selected as emission-line star candidates based on 1 micron narrow-band imaging of the cluster carried out at OPD/LNA (Brazil), and then confirmed as Wolf-Rayet stars by K-band spectroscopy performed at the 4.1 m SOAR telescope (Chile). Together with previous works, this increases the population of Wolf-Rayet stars detected in the cluster to 22 members. Moreover, it is presented for the first time a K-band spectrum of the luminous blue variable W243, which apparently implies in a higher temperature than that derived from optical spectra taken in 2003. The WC9 star WR-F was also observed, showing clear evidence of dust emission in the K-band.

AG Carinae: a Luminous Blue Variable with a high rotational velocity

We report the detection of broad absorptions due to Si IV 4088-4116 A in the Luminous Blue Variable (LBV) AG Carinae during its last hot phase (2001-2003). Our NLTE spectral analysis, with the radiative transfer code CMFGEN, revealed the photospheric nature of these lines predicting, however, much narrower and deeper absorption profiles than observed. Using a recently-developed code to compute synthetic spectra in 2D geometry allowing for the effects of rotation, we could match the broad absorptions with a high projected rotational velocity of 190 +/- 30 km/s on 2001 April. Analysis of spectra obtained on 2002 March and 2003 January, when the star was cooling, yielded to a projected rotational velocity of 110 +/- 10 km/s and 85 +/- 10 km/s, respectively. The derived rotational velocities are proportional to R^-1, as expected from angular momentum conservation. We discuss the effects of such high rotation on the spectral analysis of AG Car, and on the wind terminal velocity. Our results show direct spectroscopic evidence, for the first time, that a LBV may rotate at a significant fraction of its break-up velocity. Thus, AG Car (and possibly other LBVs) is indeed close to the Gamma-Omega limit, as predicted by theoretical studies of LBVs.