The Progenitors of Subluminous Type Ia Supernovae

We find that spectroscopically peculiar subluminous SNe Ia come from an old population. Of the sixteen subluminous SNe Ia known, ten are found in E/S0 galaxies, and the remainder are found in early-type spirals. The probability that this is a chance occurrence is only 0.2%. The finding that subluminous SNe Ia are associated with an older stellar population indicates that for a sufficiently large lookback time (already accessible in current high redshift searches) they will not be found. Due to a scarcity in old populations, hydrogen and helium main sequence stars and He red giant stars that undergo Roche lobe overflow are unlikely to be the progenitors of subluminous SNe Ia. Earlier findings that overluminous SNe Ia (dM15(B) < 0.95) come from a young progenitor population are confirmed. The fact that subluminous SNe Ia and overluminous SNe Ia come from different progenitor populations and also have different properties is a prediction of the CO white dwarf merger progenitor scenario.Comment: 7 pages, 1 figure, Accepted to ApJ Letter

The 2010 nova outburst of the symbiotic Mira V407 Cyg

The nova outburst experienced in 2010 by the symbiotic binary Mira V407 Cyg has been extensively studied at optical and infrared wavelengths with both photometric and spectroscopic observations. This outburst, reminiscent of similar events displayed by RS Oph, can be described as a very fast He/N nova erupting while being deeply embedded in the dense wind of its cool giant companion. The hard radiation from the initial thermonuclear flash ionizes and excites the wind of the Mira over great distances (recombination is observed on a time scale of 4 days). The nova ejecta is found to progressively decelerate with time as it expands into the Mira wind. This is deduced from line widths which change from a FWHM of 2760 km/s on day +2.3 to 200 km/s on day +196. The wind of the Mira is massive and extended enough for an outer neutral and unperturbed region to survive at all outburst phases.Comment: MNRAS Letter, in pres

Rates of convergence for empirical spectral measures: a soft approach

Understanding the limiting behavior of eigenvalues of random matrices is the central problem of random matrix theory. Classical limit results are known for many models, and there has been significant recent progress in obtaining more quantitative, non-asymptotic results. In this paper, we describe a systematic approach to bounding rates of convergence and proving tail inequalities for the empirical spectral measures of a wide variety of random matrix ensembles. We illustrate the approach by proving asymptotically almost sure rates of convergence of the empirical spectral measure in the following ensembles: Wigner matrices, Wishart matrices, Haar-distributed matrices from the compact classical groups, powers of Haar matrices, randomized sums and random compressions of Hermitian matrices, a random matrix model for the Hamiltonians of quantum spin glasses, and finally the complex Ginibre ensemble. Many of the results appeared previously and are being collected and described here as illustrations of the general method; however, some details (particularly in the Wigner and Wishart cases) are new. Our approach makes use of techniques from probability in Banach spaces, in particular concentration of measure and bounds for suprema of stochastic processes, in combination with more classical tools from matrix analysis, approximation theory, and Fourier analysis. It is highly flexible, as evidenced by the broad list of examples. It is moreover based largely on "soft" methods, and involves little hard analysis

V496 Scuti: An Fe II nova with dust shell accompanied by CO emission

We present near-infrared and optical observations of the nova V496 Scuti 2009 covering various phases - pre-maximum, early decline and nebular - during the first 10 months of its discovery followed by limited observations in early part of 2011 April. The spectra follow the evolution of the nova when the lines had strong P Cygni profiles to a phase dominated by prominent emission lines. The notable feature of the near-IR spectra in the early decline phase is the rare presence of first overtone bands of carbon monoxide in emission. Later about 150 days after the peak brightness the IR spectra show clear dust formation in the expanding ejecta. Dust formation in V496 Sct is consistent with the presence of lines of elements with low ionization potentials like Na and Mg in the early spectra and the detection of CO bands in emission. The light curve shows a slow rise to the maximum and a slow decline indicating a prolonged mass loss. This is corroborated by the strengthening of P Cygni profiles during the first 30 days. In the spectra taken close to the optical maximum brightness, the broad and single absorption component seen at the time of discovery is replaced by two sharper components. During the early decline phase two sharp dips that show increasing outflow velocities are seen in the P Cygni absorption components of Fe II and H I lines. The spectra in 2010 March showed the onset of the nebular phase. Several emission lines display saddle-like profiles during the nebular phase. In the nebular stage the observed fluxes of [O III] and H-beta lines are used to estimate the electron number densities and the mass of the ejecta. The optical spectra show that the nova evolved in the P_fe A_o spectral sequence. The physical conditions in the ejecta are estimated. The absolute magnitude and the distance to the nova are estimated to be M_V = -7.0 +/- 0.2 and d = 2.9 +/- 0.3 kpc respectively.Comment: 14 pages, 9 figures and 6 Tables, Accepted for Publication in MNRA

Formation of a disk structure in the symbiotic binary AX Per during its 2007-10 precursor-type activity

AX Per is an eclipsing symbiotic binary. During active phases, deep narrow minima are observed in its light curve, and the ionization structure in the binary changes significantly. From 2007.5, AX Per entered a new active phase. It was connected with a significant enhancement of the hot star wind. Simultaneously, we identified a variable optically thick warm (Teff ~ 6000 K) source that contributes markedly to the composite spectrum. The source was located at the hot star's equator and has the form of a flared disk, whose outer rim simulates the warm photosphere. The formation of the neutral disk-like zone around the accretor during the active phase was connected with its enhanced wind. We suggested that this connection represents a common origin of the warm pseudophotospheres that are indicated during the active phases of symbiotic stars.Comment: 13 pages, 9 figures, 8 tables, accepted for A&

The path to Z And-type outbursts: The case of V426 Sagittae (HBHA 1704-05)

Context. The star V426 Sge (HBHA 1704-05), originally classified as an emission-line object and a semi-regular variable, brightened at the beginning of August 2018, showing signatures of a symbiotic star outburst. Aims. We aim to confirm the nature of V426 Sge as a classical symbiotic star, determine the photometric ephemeris of the light minima, and suggest the path from its 1968 symbiotic nova outburst to the following 2018 Z And-type outburst. Methods. We re-constructed an historical light curve (LC) of V426 Sge from approximately the year 1900, and used original low- (R ∼ 500-1500; 330-880 nm) and high-resolution (R ∼ 11 000-34 000; 360-760 nm) spectroscopy complemented with Swift-XRT and UVOT, optical UBVRCIC and near-infrared JHKL photometry obtained during the 2018 outburst and the following quiescence. Results. The historical LC reveals no symbiotic-like activity from ∼1900 to 1967. In 1968, V426 Sge experienced a symbiotic nova outburst that ceased around 1990. From approximately 1972, a wave-like orbitally related variation with a period of 493.4 ± 0.7 days developed in the LC. This was interrupted by a Z And-type outburst from the beginning of August 2018 to the middle of February 2019. At the maximum of the 2018 outburst, the burning white dwarf (WD) increased its temperature to ? 2 × 105 K, generated a luminosity of ∼7 × 1037 (d/3.3 kpc)2 erg s-1 and blew a wind at the rate of ∼3 × 10-6 M yr-1. Our spectral energy distribution models from the current quiescent phase reveal that the donor is a normal M4-5 III giant characterised with Teff ∼ 3400 K, RG ∼ 106 (d/3.3 kpc) R and LG ∼ 1350 (d/3.3 kpc)2 L and the accretor is a low-mass ∼0.5 M WD. Conclusions. During the transition from the symbiotic nova outburst to the quiescent phase, a pronounced sinusoidal variation along the orbit develops in the LC of most symbiotic novae. The following eventual outburst is of Z And-type, when the accretion by the WD temporarily exceeds the upper limit of the stable burning. At this point the system becomes a classical symbiotic star.Fil: Skopal, A.. Astronomical Institute Slovak Academy Of Sciences; EslovaquiaFil: Shugarov, S. Y.. Lomonosov Moscow State University; Rusia. Astronomical Institute Slovak Academy Of Sciences; EslovaquiaFil: Munari, U.. Osservatorio Astronomico Di Padova; ItaliaFil: Masetti, N.. Inaf Istituto Di Astrofisica Spaziale E Fisica Cosmica, Bologna; Italia. Universidad Andrés Bello; ChileFil: Marchesini, Ezequiel Joaquín. Università di Torino; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Komzík, R. M.. Astronomical Institute Slovak Academy Of Sciences; EslovaquiaFil: Kundra, E.. Astronomical Institute Slovak Academy Of Sciences; EslovaquiaFil: Shagatova, N.. Astronomical Institute Slovak Academy Of Sciences; EslovaquiaFil: Tarasova, T. N.. Crimean Astrophysical Observatory Ras; RusiaFil: Buil, C.. Castanet Tolosan Observatory; FranciaFil: Boussin, C.. Observatoire de L'eridan Et de la Chevelure de Bérénice; FranciaFil: Shenavrin, V. I.. Lomonosov Moscow State University; RusiaFil: Hambsch, F. J.. Istituto Nazionale di Astrofisica; ItaliaFil: Dallaporta, S.. Istituto Nazionale di Astrofisica; ItaliaFil: Frigolé, Cecilia Andrea. Istituto Nazionale di Astrofisica; ItaliaFil: Gardey, Juan Cruz. Observatoire de la Tourbière; FranciaFil: Zubareva, A.. Institute Of Astronomy Of The Russian Academy Of Sciences; Rusia. Lomonosov Moscow State University; RusiaFil: Dubovský, P. A.. Vihorlat Observatory; EslovaquiaFil: Kroll, P.. Sonneberg Observatory; Alemani

Regulation of glucagon secretion by glucose transporter type 2 (glut2) and astrocyte-dependent glucose sensors

Ripglut1;glut2-/- mice have no endogenous glucose transporter type 2 (glut2) gene expression but rescue glucose-regulated insulin secretion. Control of glucagon plasma levels is, however, abnormal, with fed hyperglucagonemia and insensitivity to physiological hypo- or hyperglycemia, indicating that GLUT2-dependent sensors control glucagon secretion. Here, we evaluated whether these sensors were located centrally and whether GLUT2 was expressed in glial cells or in neurons. We showed that ripglut1;glut2-/- mice failed to increase plasma glucagon levels following glucoprivation induced either by i.p. or intracerebroventricular 2-deoxy-D-glucose injections. This was accompanied by failure of 2-deoxy-D-glucose injections to activate c-Fos-like immunoreactivity in the nucleus of the tractus solitarius and the dorsal motor nucleus of the vagus. When glut2 was expressed by transgenesis in glial cells but not in neurons of ripglut1;glut2-/- mice, stimulated glucagon secretion was restored as was c-Fos-like immunoreactive labeling in the brainstem. When ripglut1;glut2-/- mice were backcrossed into the C57BL/6 genetic background, fed plasma glucagon levels were also elevated due to abnormal autonomic input to the alpha cells; glucagon secretion was, however, stimulated by hypoglycemic stimuli to levels similar to those in control mice. These studies identify the existence of central glucose sensors requiring glut2 expression in glial cells and therefore functional coupling between glial cells and neurons. These sensors may be activated at different glycemic levels depending on the genetic background

Sensing the fuels: glucose and lipid signaling in the CNS controlling energy homeostasis

The central nervous system (CNS) is capable of gathering information on the body’s nutritional state and it implements appropriate behavioral and metabolic responses to changes in fuel availability. This feedback signaling of peripheral tissues ensures the maintenance of energy homeostasis. The hypothalamus is a primary site of convergence and integration for these nutrient-related feedback signals, which include central and peripheral neuronal inputs as well as hormonal signals. Increasing evidence indicates that glucose and lipids are detected by specialized fuel-sensing neurons that are integrated in these hypothalamic neuronal circuits. The purpose of this review is to outline the current understanding of fuel-sensing mechanisms in the hypothalamus, to integrate the recent findings in this field, and to address the potential role of dysregulation in these pathways in the development of obesity and type 2 diabetes mellitus