arXiv subjects

E. Aydi

Publications and source records attributed to E. Aydi.

25 records · Page 2Linked to original sources

arXiv2019

Infrared spectroscopy of the recent outburst in V1047 Cen (Nova Centauri 2005)

Fourteen years after its eruption as a classical nova (CN), V1047 Cen (Nova Cen 2005) began an unusual re-brightening in 2019 April. The amplitude of the brightening suggests that this is a dwarf nova (DN) eruption in a CN system. Very few CNe have had DN eruptions within decades of the main CN outburst. The 14 years separating the CN and DN eruptions of V1047 Cen is the shortest of all instances recorded thus far. Explaining this rapid succession of CN and DN outbursts in V1047 Cen may be challenging within the framework of standard theories for DN outbursts. Following a CN eruption, the mass accretion rate is believed to remain high $(\dot{M}\sim10^{-8}$M$_\odot$yr$^{-1})$ for a few centuries, due to the irradiation of the secondary star by the still-hot surface of the white dwarf. Thus a DN eruption is not expected to occur during this high mass accretion phase as DN outbursts, which result from thermal instabilities in the accretion disk, and arise during a regime of low mass accretion rate $(\dot{M}\sim10^{-10}$M$_\odot$yr$^{-1})$. Here we present near-infrared spectroscopy to show that the present outburst is most likely a DN eruption, and discuss the possible reasons for its early occurrence. Even if the present re-brightening is later shown to be due to a cause other than a DN outburst, the present study provides invaluable documentation of this unusual event.

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arXiv2019

Flaring, Dust Formation, And Shocks In The Very Slow Nova ASASSN-17pf (LMCN 2017-11a)

We present a detailed study of the 2017 eruption of the classical nova ASASSN-17pf (LMCN 2017-11a), which is located in the Large Magellanic Cloud, including data from AAVSO, ASAS-SN, SALT, SMARTS, SOAR, and the Neil Gehrels \textit{Swift} Observatory. The optical light-curve is characterized by multiple maxima (flares) on top of a slowly evolving light-curve (with a decline time, $t_2>$ 100 d). The maxima correlate with the appearance of new absorption line systems in the optical spectra characterized by increasing radial velocities. We suggest that this is evidence of multiple episodes of mass-ejection with increasing expansion velocities. The line profiles in the optical spectra indicate very low expansion velocities (FWHM $\sim$ 190 km s$^{-1}$), making this nova one of the slowest expanding ever observed, consistent with the slowly evolving light-curve. The evolution of the colors and spectral energy distribution show evidence of decreasing temperatures and increasing effective radii for the pseudo-photosphere during each maximum. The optical and infrared light-curves are consistent with dust formation 125 days post-discovery. We speculate that novae showing several optical maxima have multiple mass-ejection episodes leading to shocks that may drive $γ$-ray emission and dust formation.

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arXiv2018

Multiwavelength observations of V407 Lupi (ASASSN-16kt) --- a very fast nova erupting in an intermediate polar

We present a detailed study of the 2016 eruption of nova V407 Lupi (ASASSN-16kt), including optical, near-infrared, X-ray, and ultraviolet data from SALT, SMARTS, SOAR, Chandra, Swift, and XMM-Newton. Timing analysis of the multiwavelength light-curves shows that, from 168 days post-eruption and for the duration of the X-ray supersoft source phase, two periods at 565 s and 3.57 h are detected. We suggest that these are the rotational period of the white dwarf and the orbital period of the binary, respectively, and that the system is likely to be an intermediate polar. The optical light-curve decline was very fast ($t_2 \leq$ 2.9 d), suggesting that the white dwarf is likely massive ($\gtrsim 1.25$ M$_{\odot}$). The optical spectra obtained during the X-ray supersoft source phase exhibit narrow, complex, and moving emission lines of He II, also characteristics of magnetic cataclysmic variables. The optical and X-ray data show evidence for accretion resumption while the X-ray supersoft source is still on, possibly extending its duration.

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arXiv2018

What we learn from the X-ray grating spectra of Nova SMC 2016

Nova SMC 2016 has been the most luminous nova known in the direction of the Magellanic Clouds. It turned into a very luminous supersoft X-ray source between day 16 and 28 after the optical maximum. We observed it with Chandra, the HRC-S camera and the Low Energy Transmission Grating (LETG) on 2016 November and 2017 January (days 39 and 88 after optical maximum), and with XMM-Newton on 2016 December (day 75). We detected the compact white dwarf (WD) spectrum as a luminous supersoft X-ray continuum with deep absorption features of carbon, nitrogen, magnesium, calcium, probably argon and sulfur on day 39, and oxygen, nitrogen and carbon on days 75 and 88. The spectral features attributed to the WD atmosphere are all blue-shifted, by about 1800 km/s on day 39 and up to 2100 km/s in the following observations. Spectral lines attributed to low ionization potential transitions in the interstellar medium are also observed. Assuming the distance of the Small Magellanic Cloud, the bolometric luminosity exceeded Eddington level for at least three months. A preliminary analysis with atmospheric models indicates effective temperature around 700,000 K on day 39, peaking at the later dates in the 850,000-900,000 K range, as expected for a 1.25 m(sol) WD. We suggest a possible classification as an oxygen-neon WD, but more precise modeling is needed to accurately determine the abundances. The X-ray light curves show large, aperiodic ux variability, not associated with spectral variability. We detected red noise, but did not find periodic or quasi-periodic modulations.

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arXiv2017

Multiwavelength observations of nova SMCN 2016-10a --- one of the brightest novae ever observed

We report on multiwavelength observations of nova SMCN 2016-10a. The present observational set is one of the most comprehensive for any nova in the Small Magellanic Cloud, including: low, medium, and high resolution optical spectroscopy and spectropolarimetry from SALT, FLOYDS, and SOAR; long-term OGLE $V$- and $I$- bands photometry dating back to six years before eruption; SMARTS optical and near-IR photometry from $\sim$ 11 days until over 280 days post-eruption; $Swift$ satellite X-ray and ultraviolet observations from $\sim$ 6 days until 319 days post-eruption. The progenitor system contains a bright disk and a main sequence or a sub-giant secondary. The nova is very fast with $t_2 \simeq$ 4.0 $\pm$ 1.0 d and $t_3 \simeq$ 7.8 $\pm$ 2.0 d in the $V$-band. If the nova is in the SMC, at a distance of $\sim$ 61 $\pm$ 10 kpc, we derive $M_{V,\mathrm{max}} \simeq - 10.5$ $\pm$ 0.5, making it the brightest nova ever discovered in the SMC and one of the brightest on record. At day 5 post-eruption the spectral lines show a He/N spectroscopic class and a FWHM of $\sim$ 3500 kms$^{-1}$ indicating moderately high ejection velocities. The nova entered the nebular phase $\sim$ 20 days post-eruption, predicting the imminent super-soft source turn-on in the X-rays, which started $\sim$ 28 days post-eruption. The super-soft source properties indicate a white dwarf mass between 1.2 M$_{\odot}$ and 1.3 M$_{\odot}$ in good agreement with the optical conclusions.

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arXiv2016

V5852 Sgr: An Unusual Nova Possibly Associated with the Sagittarius Stream

We report spectroscopic and photometric follow-up of the peculiar nova V5852~Sgr (discovered as OGLE-2015-NOVA-01), which exhibits a combination of features from different nova classes. The photometry shows a flat-topped light curve with quasi-periodic oscillations, then a smooth decline followed by two fainter recoveries in brightness. Spectroscopy with the Southern African Large Telescope shows first a classical nova with an Fe II or Fe IIb spectral type. In the later spectrum, broad emissions from helium, nitrogen and oxygen are prominent and the iron has faded which could be an indication to the start of the nebular phase. The line widths suggest ejection velocities around $1000\,{\rm km\,s^{-1}}$. The nova is in the direction of the Galactic bulge and is heavily reddened by an uncertain amount. The $V$ magnitude 16 days after maximum enables a distance to be estimated and this suggests that the nova may be in the extreme trailing stream of the Sagittarius dwarf spheroidal galaxy. If so it is the first nova to be detected from that, or from any dwarf spheroidal galaxy. Given the uncertainty of the method and the unusual light curve we cannot rule out the possibility that it is in the bulge or even the Galactic disk behind the bulge.

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arXiv2014

Automated procedure to derive fundamental parameters of B and A stars: Application to the young cluster NGC 3293

This work describes a procedure to derive several fundamental parameters such as the effective temperature, surface gravity, equatorial rotational velocity and microturbulent velocity. In this work, we have written a numerical procedure in Python which finds the best fit between a grid of synthetic spectra and the observed spectra by minimizing a standard chi-square. LTE model atmospheres were calculated using the ATLAS9 code and were used as inputs to the spectrum synthesis code SYNSPEC48 in order to compute a large grid of synthetic Balmer line profiles. This new procedure has been applied to a large number of new observations (GIRAFFE spectra) of B and A stars members of the young open cluster NGC3293. These observations are part of the GAIA ESO Survey. Takeda's procedure was also used to derive rotational velocities and microturbulent velocities. The results have been compared to previous determinations by other authors and are found to agree with them. As a first result, we concluded that using this procedure, an accuracy of +-200 K could be achieved in effective temperature and +-0.2 dex in surface gravities.

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