Search

the ANS Collaboration uses the UBV RCIC filters from various commercial manufacturers (Omega Optical, Custom Scientific, Schuler, Optec, Astrodon) for its ongoing photometric monitoring of symbiotic stars. We measured their transmittance profiles over the range 2000 Å to 1.1 μm for various operating conditions, and we are monitoring their evolution over time. Their field performance in terms of color equations has been evaluated by analyzing the transformations from local to standard system of the 14602 observing runs so far collected on symbiotic stars with the ANS Collaboration telescopes. Ageing effects, red leaks and transmittance vs. angle of incidence are also evaluated.

ANS Collaboration is a growing Italian network of small and medium size telescopes performing spectroscopy (low and medium resolution single dispersion, and Echelle high resolution modes) and UBV RCIC CCD photometry of symbiotic stars and novae mainly, but with interest also on other types of objects like optical transients, eclipsing binaries, X-ray source counterparts and on-call follow-up observations of selected targets from some surveys like IPHAS or RAVE. In the present form ANS started operations in 2005, and at the time of writing has logged on symbiotic stars 14602 photometric runs and a rich ensemble of low and high resolution, absolutely fluxed spectra. the paper describes the internal organization, operation modes and procedures, and presents sample data and performance statistics.

We reconstructed photometric histories of symbiotic stars and novae from direct inspection and measurement of photographic plates preserved at historical archives. We have completed the digging of the rich Asiago archive, and have started working on the Harvard plate stack, while other plate collections should be added soon. For homogeneity, we use the same UBV RCIC photometric comparison sequences used in current CCD observations. This data harvest has permitted the discovery of past undetected outbursts and secular trends, or to derive previously unknown orbital periods and recurrence times, which are essential to constrain the nature of these capricious and variegated active binaries.

Our photometric and spectroscopic monitoring shows that starting with 2020 June 4, day  +217 from optical maximum and well into its advanced nebular stage, Nova Scuti (Nova Sct) 2019 begun displaying a series of nine large amplitude flares (up to |$\Delta m \sim 1.7$|  mag), characterized by a rapid rise to peak (≤10 h) and a fast exponential decline (e -folding time ∼50 h). The time interval Δ t between flares follows an ordered sequence, declining from 8.43 to 4.90 d, that safely allows to exclude that any other flare occurred without being recorded by the observations. When the sequence of flares was over by 2020 July 28 (day  +271), Nova Sct 2019 slowed its overall decline rate from Δ m  = 0.0067 to 0.0027 mag d−1. The flares were caused by material expelled at high velocity (∼1000 km s−1) from the still burning white dwarf (WD). The cooler pseudo-photosphere forming at each flare in the expelled material, resulted in a recombination wave to spread through the original nova ejecta (at ∼170 au from the WD), quenching emission from [Fe  x ] and [Fe  vii ] and boosting that from lower ionization species. After each flare, once the small amount of expelled material had turned optically thin, the original nova ejecta resumed displaying [Fe  x ] and [Fe  vii ] emission lines, a fact that clearly proves the direct photoionization action exerted on the ejecta by the burning WD. While the other known flaring novae (V458 Vul, V4745 Sgr, and V5588 Sgr) presented the flares close to maximum brightness and with increasing Δ t , Nova Sct 2019 is unique in having displayed them during the advanced nebular stage and with decreasing Δ t. [ABSTRACT FROM AUTHOR]

There are indications that the third-known eruption of the recurrent nova T CrB is imminent, and multiwavelength observations prior to the eruption are important to characterize the system before it erupts. T CrB is known to display the SiO fundamental vibrational feature at 8  |$\, \mu$| m. When the anticipated eruption occurs, it is possible that the shock produced when the ejected material runs into the wind of the red giant in the system may be traced using SiO maser emission. We have used the 100 m Effelsberg Radio Telescope to search for 28SiO emission in the υ = 1, υ = 2, J = 1 → 0 transitions, at 43.122 GHz and 42.820 GHz, respectively, while the system is in quiescence. We find no evidence for such emission. We set stringent 3σ upper limits of 1.66 mJy on emission in the υ = 1, J = 1 → 0 transition, and 1.72 mJy in the υ = 2, J = 1 → 0 transition, respectively, for a noise bandwidth of 250 kHz. The corresponding limits for a 31.25 kHz bandwidth are 4.69 and 4.86 mJy, respectively. These upper limits improve on previous upper limits for this system by more than two orders of magnitude. [ABSTRACT FROM AUTHOR]

On 2021 August 8, the recurrent nova RS Ophiuchi (RS Oph) erupted again, after an interval of 15.5 yr. Regular monitoring by the Neil Gehrels Swift Observatory began promptly, on August 9.9 (0.37 d after the optical peak), and continued until the source passed behind the Sun at the start of November, 86 d later. Observations then restarted on day 197, once RS Oph emerged from the Sun constraint. This makes RS Oph the first Galactic recurrent nova to have been monitored by Swift throughout two eruptions. Here we investigate the extensive X-ray data sets between 2006 and 2021, as well as the more limited data collected by the European X-ray Observatory Satellite (EXOSAT) in 1985. The hard X-rays arising from shock interactions between the nova ejecta and red giant wind are similar following the last two eruptions. In contrast, the early supersoft source (SSS) in 2021 was both less variable and significantly fainter than in 2006. However, 0.3–1 keV light curves from 2021 reveal a 35 s quasi-periodic oscillation consistent in frequency with the 2006 data. The Swift X-ray spectra from 2021 are featureless, with the soft emission typically being well parametrized by a simple blackbody, while the 2006 spectra showed much stronger evidence for superimposed ionized absorption edges. Considering the data after day 60 following each eruption, during the supersoft phase the 2021 spectra are hotter, with smaller effective radii and lower wind absorption, leading to an apparently reduced bolometric luminosity. We explore possible explanations for the gross differences in observed SSS behaviour between the 2006 and 2021 outbursts. [ABSTRACT FROM AUTHOR]

We report the determination of abundances and isotopic ratios for C, O, and Si in the photosphere of the red giant (RG) component of the recurrent nova (RN) T Coronae Borealis from new 2.284–2.402 μ m and 3.985–4.155 μ m spectroscopy. Abundances and isotopic ratios in the photosphere may be affected by (i) processes in the RG interior which are brought to the surface during dredge-up and (ii) contamination of the RG, either during the common envelope phase of the binary evolution or by material synthesized in RN eruptions, or a combination of the two. We find that the abundances of C, O, and Si are reasonably consistent with the expected composition of an RG after first dredge-up, as is the 16O/17O ratio. The 28Si/29Si ratio is found to be 8.6 ± 3.0, and that for 28Si/30Si is 21.5 ± 3.0. The 12C/13C ratio (10 ± 2) is somewhat lower than expected for first dredge-up. The 16O/18O ratio (41 ± 3) is highly inconsistent with that expected either from RG evolution (∼550) or from contamination of the RG by the products of a nova thermonuclear runaway. In particular, the C and O isotopic ratios taken in combination are a puzzle. We urge confirmation of our results using spectroscopy at high resolution. We also encourage a thorough theoretical study of the effects on the secondary star in an RN system of contamination by ejecta having anomalous abundances and isotopic ratios. [ABSTRACT FROM AUTHOR]

We present a comprehensive review of all observations of the eclipsing recurrent Nova LMC 1968 in the Large Magellanic Cloud which was previously observed in eruption in 1968, 1990, 2002, 2010, and most recently in 2016. We derive a probable recurrence time of 6.2 ± 1.2 yr and provide the ephemerides of the eclipse. In the ultraviolet–optical–IR photometry the light curve shows high variability right from the first observation around 2 d after eruption. Therefore no colour changes can be substantiated. Outburst spectra from 2016 and 1990 are very similar and are dominated by H and He lines longward of 2000 Å. Interstellar reddening is found to be E (B − V) = 0.07 ± 0.01. The super soft X-ray luminosity is lower than the Eddington luminosity and the X-ray spectra suggest the mass of the white dwarf (WD) is larger than 1.3 M⊙. Eclipses in the light curve suggest that the system is at high orbital inclination. On day 4 after the eruption a recombination wave was observed in Fe  ii ultraviolet absorption lines. Narrow-line components are seen after day 6 and explained as being due to reionization of ejecta from a previous eruption. The UV spectrum varies with orbital phase, in particular a component of the He  ii  1640 Å emission line, which leads us to propose that early-on the inner WD Roche lobe might be filled with a bound opaque medium prior to the re-formation of an accretion disc. Both this medium and the ejecta can cause the delay in the appearance of the soft X-ray source. [ABSTRACT FROM AUTHOR]

We report the discovery of the diatomic molecule SiO in the gas phase in the environment of the recurrent nova T Coronae Borealis. While some of the SiO is photospheric, a substantial portion must arise in the wind from the red giant component of T CrB. A simple fit to the SiO feature, assuming local thermodynamic equilibrium, suggests a SiO column density of 2.8 × 1017 cm−2 and temperature ∼1000 K; the SiO column density is similar to that present in the winds of field red giants. A search for SiO maser emission is encouraged both before and after the next anticipated eruption. We find that the 12C/13C ratio in the red giant is <9, with a best-fitting value of ∼5, a factor ∼18 times lower than the solar value of 89. We find no convincing evidence for the presence of dust in the environment of T CrB, which we attribute to the destructive effects on nucleation sites of hard X-ray emission. When the next eruption of T CrB occurs, the ejected material will shock the wind, producing X-ray and coronal line emission, as is the case for the recurrent nova RS Oph. T CrB is also a good candidate for very high energy γ-ray emission, as first observed during the 2010 outburst of V407 Cyg. We include in the paper a wide variety of infrared spectroscopic and photometric data. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) and optical photometry and spectroscopy are presented for the nova V1831 Aquilae, covering the early decline and dust-forming phases during the first ∼90 d after its discovery. The nova is highly reddened due to interstellar extinction. Based solely on the nature of the NIR spectrum, we are able to classify the nova to be of the Fe II class. The distance and extinction to the nova are estimated to be 6.1 ± 0.5 kpc and Av ∼ 9.02, respectively. Lower limits of the electron density, emission measure and ionized ejecta mass are made from a Case B analysis of the NIR Brackett lines, while the neutral gas mass is estimated from the optical [O I] lines. We discuss the cause of the rapid strengthening of the He I 1.0830-μm line during the early stages. V1831 Aql formed a modest amount of dust fairly early (∼19.2 d after discovery); the dust shell is not seen to be optically thick. Estimates of the dust temperature, dust mass and grain size are made. Dust formation commences around day 19.2 at a condensation temperature of 1461 ± 15 K, suggestive of a carbon composition, following which the temperature is seen to decrease gradually to 950 K. The dust mass shows a rapid initial increase, which we interpret as being due to an increase in the number of grains, followed by a period of constancy, suggesting the absence of grain destruction processes during this latter time. A discussion of the evolution of these parameters is made, including certain peculiarities seen in the grain radius evolution. [ABSTRACT FROM AUTHOR]

After 26 years from the major event of 1990, in early 2016 the puzzling symbiotic binary MWC 560 has gone into a new and even brighter outburst. We present our tight BVR C I C photometric monitoring of MWC 560 (451 independent runs distributed over 357 different nights), covering the 2005–2016 interval, and the current outburst in particoular. A stricking feature of the 2016 outburst has been the suppression of the short term chaotic variability during the rise toward maximum brightness, and its dominance afterward with an amplitude in excess of 0.5 mag. Similar to the 1990 event when the object remained around maximum brightness for ∼6 months, at the time Solar conjunction prevented further observations of the current outburst, MWC 560 was still around maximum, three months past reaching it. We place our observations into a long term contex by combining with literature data to provide a complete 1928–2016 lightcurve. Some strong periodicities are found to modulate the optical photometry of MWC 560. A period of 1860 days regulate the occourence of bright phases at BVR C bands (with exactly 5.0 cycles separating the 1990 and 2016 outbursts), while the peak brightness attained during bright phases seems to vary with a ∼9570 days cycle. A clean 331 day periodicity modulate the I C lightcurve, where the emission from the M giant dominates, with a lightcurve strongly reminiscent of an ellipsoidal distortion plus irradiation from the hot companion. Pros and cons of 1860 and 331 days as the system orbital period are reviewed, waiting for a spectroscopic radial velocity orbit of the M giant to settle the question (provided the orbit is not oriented face-on). [ABSTRACT FROM AUTHOR]

We have monitored the 2014 superoutburst of the WZ Sge-type transient PNV J03093063+2638031 for more than four months, from V = 11.0 maximum brightness down to V = 18.4 mag, close to quiescence value, by obtaining BVRCIC photometry and low resolution fluxed spectroscopy. The evolution was normal and no late-time "echo" outbursts were observed. The absolute integrated flux of emission lines kept declining along the superoutburst, and their increasing contrast with the underlying continuum was simply the result of the faster decline of the continuum compared to the emission lines. Inspection of historical Harvard plates covering the 1899-1981 period did not reveal previous outbursts, neither "normal" nor "super". We discovered an extended emission nebula (radius ~1 arcmin) around PNV J03093063+2638031, that became visible for a few months as the result of photo-ionization from the superoutburst of the central star. The nebula is not present on Palomar I and II sky survey images and it quickly disappeared when the outburst was over. From the rate at wich the ionization front swept through the nebula, we derive a distance of ~120 pc to the system. The nebula is density bounded with an outer radius of 0.03 pc, and the absolute magnitude of the central star in quiescence is MV ~ 14.2 mag. The electron density in the nebula is estimated to be 105 cm-3 from the observed recombination time scale. Given the considerable substructures seen across the nebula, a low filling factor is inferred. Similar nebulae have not been reported for other WZ Sge objects and the challenges posed to models are considered. [ABSTRACT FROM AUTHOR]

We present optical spectroscopy collected at seven epochs and BVRCIC photometry obtained at 1227 epochs of nova V723 Cas, covering the time interval between 2007 and 2015. The mean magnitude during this period, stable at ~3 mag brighter than in quiescence, and the continuous presence of strong [Fe X] and other high-ionization emission lines, indicates that the nuclear burning at the surface of the white dwarf is continuing 20 years past the initial outburst. The light curve shows a large amplitude (2 mag) orbital modulation, which is governed by the visibility of the irradiated side of the secondary star. Our observations do not confirm the reported increase with time of the orbital period of V723 Cas, a period of P=16.638 383 ± 0.000 025 h satisfying equally well all available observations in all bands. Our observations also do not confirm the presence of an additional periodicity around P=15.2397 h from which V723 Cas was classified as an intermediate-polar system. [ABSTRACT FROM AUTHOR]

The outburst of Nova Sgr 2011 N.2 (=V5588 Sgr) was followed with optical and near-IR photometric and spectroscopic observations for 3.5 yr, beginning shortly before the maximum. V5588 Sgr is located close to Galactic Centre, suffering from E(B -- V) = 1.56 (±0.1) extinction. The primary maximum was reached at V = 12.37 on UT 2011 April 2.5 (±0.2), and the underlying smooth decline was moderately fast with t2V = 38 and t3V = 77 d. On top of an otherwise normal decline, six self-similar, fast evolving and bright secondary maxima (SdM) appeared in succession. Only very few other novae have presented so clear SdM. Both the primary maximum and all SdM occurred at later times with increasing wavelengths, by amounts in agreement with expectations from fireball expansions. The radiative energy released during SdM declined following an exponential pattern, while the breadth of individual SdM and the time interval between them widened. Emission lines remained sharp (FWHM ~ 1000 km s-1) throughout the whole nova evolution, with the exception of a broad pedestal with a trapezoidal shape (Δvel = 3600 km s-1 at the top and 4500 km s-1 at the bottom) which was only seen during the advanced decline from SdM maxima and was absent in between SdM. V5588 Sgr at maximum light displayed a typical Fe II-class spectrum which did not evolve into a nebular stage. About 10 d into the decline from primary maximum, a typical high-ionization He/N-class spectrum appeared and remained visible simultaneously with the Fe n-class spectrum, qualifying V5588 Sgr as a rare hybrid nova. While the Fe n-class spectrum faded into oblivion, the He/N-class spectrum developed strong [Fex] coronal lines. [ABSTRACT FROM AUTHOR]

We present outburst and quiescence spectra of the classical nova KT Eri and discuss the appearance of a sharp HeII 4686 Å emission line, whose origin is a matter of discussion for those novae that showed a similar component. We suggest that the sharp HeII line, when it first appeared toward the end of the outburst optically thick phase, comes from the wrist of the dumbbell structure characterizing the ejecta. When the ejecta turned optically thin, the already sharp HeII line became two times narrower and originated from the exposed central binary. During the optically thin phase, the HeII line displayed a large change in radial velocity that had no counterpart in the Balmer lines (both their narrow cores and the broad pedestals). The large variability in radial velocity of the HeII line continued well into quiescence, and it remains the strongest emission line observed over the whole optical range. [ABSTRACT FROM AUTHOR]

Context. Nova Eridani (2009) caught the eye of the nova community due to its fast decline from maximum, which was initially missed, and its subsequent development in the radio and X-ray wavelengths. This system also exhibits properties similar to those of the much smaller class of recurrent novae; themselves potential progenitors of type Ia supernovae. Aims. We aim to determine the nature and physical parameters of the KT Eri progenitor system. Methods. We searched the Harvard College Observatory archive plates for the progenitor of KT Eri to determine the nature of the system, particularly the evolutionary stage of the secondary. We used the data obtained to search for any periodic signal and the derived luminosity to estimate a recurrence timescale. Furthermore, by comparing the colours of the quiescent system on a colour-magnitude diagram we may infer the nature of the secondary star. Results. We identified the progenitor system of KT Eri and measured a quiescent magnitude of (B) = 14.7 ± 0.4. No previous outburst was found. However, we suggest that if the nova is recurrent it should be on a timescale of centuries. We find a periodicity at quiescence of 737 days which may arise from reflection effects and/or eclipses in the central binary. The periodicity and the quiescence magnitude of the system suggest that the secondary star is evolved and likely in, or ascending, the Red Giant Branch. A second period is evident at 376 days which has a sinusoidal like light curve. Furthermore, the outburst amplitude of ∼9 mag is inconsistent with those expected for fast classical novae (∼17 mag) which may lend further support for an evolved secondary. Conclusions. We investigated the probable recurrent nova KT Eri for which we suggest an inter-outburst period of order centuries and an evolved secondary. This may suggest that there is a whole range of possible inter-outburst periods in between the "typical" classical and recurrent novae nomenclature. Archival searches are an excellent tool in order to investigate the nature of astrophysical objects, in order to determine the nature and physical parameters. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the early phases of the ongoing outburst that CI Cyg, a prototype symbiotic star, is currently undergoing after 30-year quiescence. We have tightly monitored CI Cyg in bands, starting a whole year before the onset of the outburst, and in addition we obtained numerous Echelle high- and low-resolution absolutely flux-calibrated spectra. The outburst started while the accreting white dwarf (WD) was being eclipsed by the Roche lobe filling M giant companion, and it was discovered during the egress phase on the second half of 2008 August. The system reached peak V-band brightness in early 2008 October and has been characterized by amplitudes mag. At maximum V-band brightness, the outbursting WD had expanded to closely resemble an F3 II/Ib star, with and . The high-ionization emission lines ([Ne v], [Fe vii], He ii) disappeared and only lower ionization lines were visible. Balmer and He i emission lines declined in equivalent width but increased in absolute flux. The output radiated by the hot component during the outburst corresponds to nuclear burning proceeding at a rate. [ABSTRACT FROM AUTHOR]

The moderately fast Nova Oph 2007 reached maximum brightness on 2007 March 28 at and , after fast initial rise and a pre-maximum halt lasting a week. Decline times were and d. The distance to the nova is , the height above the Galactic plane is , the reddening is and the absolute magnitude at maximum is and . The spectrum four days before maximum resembled a F6 supergiant, in an agreement with broad-band colours. It later developed into that of a standard ‘Fe ii’-class nova. Nine days past maximum, the expansion velocity estimated from the width of Hα emission component was , and the displacement from it of the principal and diffuse-enhanced absorption systems was ∼650 and , respectively. Dust probably formed and disappeared during the period from 82 to 100 d past maximum, causing (at peak dust concentration) an extinction of mag and an extra reddening. [ABSTRACT FROM AUTHOR]

Our CCD photometry of Nova Scuti 2005 N.1 shows it to be a fast nova, characterized by and , affected by an mag reddening, appearing at a position (±0.04 arcsec) (±0.09 arcsec, J2000) and peaking at mag on ∼September 28.1ut. Absolute spectrophotometry places it within the Fe ii class. The profile of emission lines is characterized by a double peak with a velocity separation of 690 km s−1 and a width at half intensity of 1200 km s−1. The distance to the nova is , and its height above the Galactic plane is pc. The highly crowded field affects a possible identification of the progenitor, whose pre-outburst magnitude should, however, have been mag, thus below the limit of photographic surveys. A deep photometric sequence is provided to support continued observations of the advanced decline phases. [ABSTRACT FROM AUTHOR]