We obtained the absolute magnitudes, distances, and white dwarf (WD) masses of 32 recent galactic novae based on the time-stretching method for nova light curves. A large part of the light/color ...curves of two classical novae often overlap each other if we properly squeeze/stretch their timescales. Then, a target nova brightness is related to the other template nova brightness by , where t is the time, MVt is the absolute V magnitude, and fs is their timescaling ratio. Moreover, when these two time-stretched light curves, (t/fs)-(MV − 2.5 log fs), overlap each other, (t/fs)-(B − V)0 do too, where (B − V)0 is the intrinsic B − V color. Thus, the two nova tracks overlap each other in the (B − V)0-(MV − 2.5 log fs) diagram. Inversely, using these properties, we obtain/confirm the distance and reddening by comparing each nova light/color curves with well-calibrated template novae. We classify the 32 novae into two types, LV Vul and V1500 Cyg, in the time-stretched (B − V)0-(MV − 2.5 log fs) color-magnitude diagram. The WD mass is obtained by direct comparison of the model V light curves with the observation. Thus, we obtain a uniform set of 32 galactic classical novae that provides the distances and WD masses from a single method. Many novae broadly follow the universal decline law and the present method can be applied to them, while some novae largely deviate from the universal decline law and so the method cannot be directly applied to them. We discuss such examples.
Many kinds of transporters contribute to glutamatergic excitatory synaptic transmission. Glutamate is loaded into synaptic vesicles by vesicular glutamate transporters to be released from presynaptic ...terminals. After synaptic vesicle release, glutamate is taken up by neurons or astrocytes to terminate the signal and to prepare for the next signal. Glutamate transporters on the plasma membrane are responsible for transporting glutamate from extracellular fluid to cytoplasm. Glutamate taken up by astrocyte is converted to glutamine by glutamine synthetase and transported back to neurons through glutamine transporters on the plasma membranes of the astrocytes and then on neurons. Glutamine is converted back to glutamate by glutaminase in the neuronal cytoplasm and then loaded into synaptic vesicles again. Here, the structures of glutamate transporters and glutamine transporters, their conformational changes, and how they use electrochemical gradients of various ions for substrate transport are summarized. Pharmacological regulations of these transporters are also discussed.
Abstract
YZ Ret is the first X-ray flash detected classical nova, and is also observed in optical, X-ray, and gamma-ray. We propose a comprehensive model that explains the observational properties. ...The white dwarf mass is determined to be ∼1.33
M
☉
, which reproduces the multiwavelength light curves of YZ Ret, from optical, X-ray, to gamma-ray. We show that a shock is naturally generated far outside the photosphere because winds collide with themselves. The derived lifetime of the shock explains some of the temporal variations of emission lines. The shocked shell significantly contributes to the optical flux in the nebular phase. The decline trend of shell emission in the nebular phase is close to ∝
t
−1.75
and the same as the universal decline law of classical novae, where
t
is the time from the outburst.
We analyzed optical, UV, and X-ray light curves of 14 recurrent and very fast novae in our Galaxy, Magellanic Clouds, and M31, and obtained their distances and white dwarf (WD) masses. Among the 14 ...novae, we found that eight novae host very massive ( 1.35 M☉) WDs and are candidates for Type Ia supernova (SN Ia) progenitors. We confirmed that the same timescaling law and time-stretching method as in galactic novae can be applied to extragalactic fast novae. We classify the four novae V745 Sco, T CrB, V838 Her, and V1534 Sco as V745 Sco type (rapid decline); the two novae RS Oph and V407 Cyg as RS Oph type (circumstellar matter (CSM) shock); and the two novae U Sco and CI Aql as U Sco type (normal decline). The V light curves of these novae almost overlap with each other in the same group, if we properly stretch in the time direction (timescaling law). We apply our classification method to the Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and M31 novae. YY Dor, LMC N 2009a, and SMC N 2016 belong to the normal-decline type, LMC N 2013 to the CSM-shock type, and LMC N 2012a and M31 N 2008-12a to the rapid-decline type. We obtained the distance to SMC N 2016 to be d = 20 2 kpc, suggesting that SMC N 2016 is a member of our Galaxy. Rapid-decline type novae have very massive WDs of MWD = 1.37-1.385 M☉ and are promising candidates for SN Ia progenitors. Novae of this type are much fainter than the maximum magnitude versus rate of decline relations.
Abstract
CN Cha is a slow symbiotic nova characterized by a 3 yr long optical flat peak followed by a rapid decline. We present theoretical light curves for CN Cha, based on hydrostatic ...approximation, and estimate the white-dwarf (WD) mass to be ∼0.6
M
☉
for a low metal abundance of
Z
= 0.004. These kinds of flat-peak novae are border objects between classical novae having a sharp optical peak and extremely slow novae, the evolutions of which are too slow to be recognized as nova outbursts on a human timescale. Theoretically, there are two types of nova envelope solutions—static and optically thick wind—in low-mass WDs (≲0.7
M
☉
). Such a nova outburst begins first in a hydrostatic manner, and later it could change to an optically thick wind evolution, due to perturbation by the companion star in the nova envelope. Multiple peaks are a reflection of the relaxation process of the transition. CN Cha supports our explanation of the difference between long-lasting flat-peak novae like CN Cha and multiple-peak novae like V723 Cas, because the companion star is located far outside, and does not perturb, the nova envelope in CN Cha.
LIGHT-CURVE ANALYSIS OF NEON NOVAE Hachisu, Izumi; Kato, Mariko
Astrophysical journal/The Astrophysical journal,
01/2016, Letnik:
816, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We analyzed light curves of five neon novae, QU Vul, V351 Pup, V382 Vel, V693 CrA, and V1974 Cyg, and determined their white dwarf (WD) masses and distance moduli on the basis of theoretical ...light curves composed of free-free and photospheric emission. For QU Vul, we obtained a distance of d ∼ 2.4 kpc, reddening of E(B − V) ∼ 0.55, and WD mass of MWD = 0.82- . This suggests that an oxygen-neon WD lost a mass of more than since its birth. For V351 Pup, we obtained , , and - . For V382 Vel, we obtained , , and - . For V693 CrA, we obtained , , and - . For V1974 Cyg, we obtained , , and - . For comparison, we added the carbon-oxygen nova V1668 Cyg to our analysis and obtained , , and - . In QU Vul, photospheric emission contributes 0.4-0.8 mag at most to the optical light curve compared with free-free emission only. In V351 Pup and V1974 Cyg, photospheric emission contributes very little (0.2-0.4 mag at most) to the optical light curve. In V382 Vel and V693 CrA, free-free emission dominates the continuum spectra, and photospheric emission does not contribute to the optical magnitudes. We also discuss the maximum magnitude versus rate of decline relation for these novae based on the universal decline law.
We analyzed light curves of seven relatively slower novae, PW Vul, V705 Cas, GQ Mus, RR Pic, V5558 Sgr, HR Del, and V723 Cas, based on an optically thick wind theory of nova outbursts. For fast ...novae, free-free emission dominates the spectrum in optical bands rather than photospheric emission, and nova optical light curves follow the universal decline law. We calculated three model light curves of free-free emission, photospheric emission, and their sum for various white dwarf (WD) masses with various chemical compositions of their envelopes and fitted reasonably with observational data of optical, near-IR (NIR), and UV bands. From light curve fittings of the seven novae, we estimated their absolute magnitudes, distances, and WD masses. In PW Vul and V705 Cas, free-free emission still dominates the spectrum in the optical and NIR bands. We also discussed the reason why the very slow novae are about ~1 mag brighter than the proposed maximum magnitude versus rate of decline relation.
We propose a modified color-magnitude diagram for novae in outburst, i.e., (B − V)0 versus (MV − 2.5 log fs), where fs is the time-scaling factor of a (target) nova against a comparison (template) ...nova, (B − V)0 is the intrinsic B − V color, and MV is the absolute V magnitude. We dub it the time-stretched color-magnitude diagram. We carefully reanalyzed 20 novae based on the time-stretching method and revised their extinctions E(B − V), distance moduli in the V-band (m − M)V, distances d, and time-scaling factors fs against the template nova LV Vul. We have found that these 20 nova outburst tracks broadly follow one of the two template tracks, the LV Vul/V1668 Cyg or V1500 Cyg/V1974 Cyg group, in the time-stretched color-magnitude diagram. In addition, we estimate the white dwarf masses and (m − M)V of the novae by directly fitting the absolute V model light curves (MV) with observational apparent V magnitudes (mV). A good agreement of the two estimates of (m − M)V confirms the consistency of the time-stretched color-magnitude diagram. Our distance estimates are in good agreement with the results of Gaia Data Release 2.
ABSTRACT We have examined the outburst tracks of 40 novae in the color-magnitude diagram (intrinsic B − V color versus absolute V magnitude). After reaching the optical maximum, each nova generally ...evolves toward blue from the upper right to the lower left and then turns back toward the right. The 40 tracks are categorized into one of six templates: very fast nova V1500 Cyg; fast novae V1668 Cyg, V1974 Cyg, and LV Vul; moderately fast nova FH Ser; and very slow nova PU Vul. These templates are located from the left (blue) to the right (red) in this order, depending on the envelope mass and nova speed class. A bluer nova has a less massive envelope and faster nova speed class. In novae with multiple peaks, the track of the first decay is more red than that of the second (or third) decay, because a large part of the envelope mass had already been ejected during the first peak. Thus, our newly obtained tracks in the color-magnitude diagram provide useful information to understand the physics of classical novae. We also found that the absolute magnitude at the beginning of the nebular phase is almost similar among various novae. We are able to determine the absolute magnitude (or distance modulus) by fitting the track of a target nova to the same classification of a nova with a known distance. This method for determining nova distance has been applied to some recurrent novae, and their distances have been recalculated.
Abstract The classical nova V339 Del 2013 is characterized by a 1.5 mag dip of the V light curve owing to a dust shell formation, with which soft X-ray emissions coexist. We present a Strömgren y ...-band light curve, which represents continuum emission, not influenced by strong O iii emission lines. The y light curve monotonically decreases in marked contrast to the V light curve that shows a 1.5 mag dip. We propose a multiwavelength light-curve model that reproduces the y and V light curves as well as the gamma-ray and X-ray light curves. In our model, a strong shock arises far outside the photosphere after optical maximum, because later ejected matter collides with earlier ejected gas. Our shocked shell model explains optical emission lines, H α , hard X-ray, and gamma-ray fluxes. A dust shell forms behind the shock that suppresses O iii . This low flux of O iii shapes a 1.5 mag drop in the V light curve. Then, the V flux recovers with an increasing contribution from O iii lines, while the y flux does not. However, the optical depth of the dust shell is too small to absorb the photospheric (X-ray) emission of the white dwarf. This is the reason that a dust shell and soft X-ray radiation coexist. We determined the white dwarf mass to be M WD = 1.25 ± 0.05 M ☉ and the distance modulus in the V band to be ( m − M ) V = 12.2 ± 0.2; the distance is d = 2.1 ± 0.2 kpc for the reddening of E ( B − V ) = 0.18.
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