Two New Nova Shells associated with V4362 Sagittarii and DO Aquilae

A classical nova is an eruption on the surface of a white dwarf in an accreting binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell. The shaping mechanisms of nova shells are probes of the processes that take place at energy scales between planetary nebulae and supernova remnants. We report on the discovery of nova shells surrounding the post-nova systems V4362 Sagittarii (1994) and more limited observations of DO Aquilae (1925). Distance measurements of 0.5p/m1.4 kpc for V4362 Sgr and 6.7 p/m 3.5 kpc -0.2 for DO Aql are found based on the expansion parallax method. The growth rates are measured to be 0.07``/year for DO Aql and 0.32``/year for V4362 Sgr. A preliminary investigation into the ionisation structure of the nova shell associated with V4362 Sgr is presented. The observed ionisation structure of nova shells depends strongly on their morphology and the orientation of the central component towards the observer. X-ray, IR and UV observations as well as optical integral field unit spectroscopy are required to better understand these interesting objects

Discovery of an optical cocoon tail behind the runaway HD 185806

Studies on the circumstellar structures around evolved stars provide vital information on the evolution of the parent star and the properties of the local interstellar medium. In this work, we present the discovery and characterization of an optical cocoon tail behind the star HD 185806. The cocoon apex emission is puzzling, as it is detected in the infrared but shows no signal in the optical wavelength. The H-alpha and [OIII] fluxes of the nebular structure vary from 2.7 to 8.5x10^{-12} erg s^{-1} cm^ {-2} and from 0.9 to 7.0x10^{-13} erg s^{-1} cm^{-2}, respectively. Through high-resolution spectroscopy, we derive the spectral type of the star, construct the position-velocity diagrams of the cocoon tail for the H-alpha, [OIII] and [NII] emission lines, and determine its velocity in the range of -100 to 40 km s ^{-1} . Furthermore, we use SED fitting and MESA evolutionary models adopting a distance of 900 pc, and classify HD 185806 as a 1.3 M star, in the transition phase between the RGB and early AGB stages. Finally, we study the morpho-kinematic structure of the cocoon tail using the astronomical software SHAPE. An ellipsoidal structure, with an inclination of 19 degrees with respect to the plane of sky is found to better reproduce the observed cocoon tail of HD 185806.Comment: Accepted 2022 June 29. Received 2022 June 24; in original form 2022 May 26, 14 pages. Dedicated to V.G. who passed away on 2 Sept. 202

Comparative performance of selected variability detection techniques in photometric time series

Photometric measurements are prone to systematic errors presenting a challenge to low-amplitude variability detection. In search for a general-purpose variability detection technique able to recover a broad range of variability types including currently unknown ones, we test 18 statistical characteristics quantifying scatter and/or correlation between brightness measurements. We compare their performance in identifying variable objects in seven time series data sets obtained with telescopes ranging in size from a telephoto lens to 1m-class and probing variability on time-scales from minutes to decades. The test data sets together include lightcurves of 127539 objects, among them 1251 variable stars of various types and represent a range of observing conditions often found in ground-based variability surveys. The real data are complemented by simulations. We propose a combination of two indices that together recover a broad range of variability types from photometric data characterized by a wide variety of sampling patterns, photometric accuracies, and percentages of outlier measurements. The first index is the interquartile range (IQR) of magnitude measurements, sensitive to variability irrespective of a time-scale and resistant to outliers. It can be complemented by the ratio of the lightcurve variance to the mean square successive difference, 1/h, which is efficient in detecting variability on time-scales longer than the typical time interval between observations. Variable objects have larger 1/h and/or IQR values than non-variable objects of similar brightness. Another approach to variability detection is to combine many variability indices using principal component analysis. We present 124 previously unknown variable stars found in the test data.Comment: 29 pages, 8 figures, 7 tables; accepted to MNRAS; for additional plots, see http://scan.sai.msu.ru/~kirx/var_idx_paper

Two new nova shells associated with V4362 Sagittarii and DO Aquilae

A classical nova is an eruption on the surface of a white dwarf in an accreting binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell. The shaping mechanisms of nova shells are probes of the processes that take place at energy scales between planetary nebulae and supernova remnants. We report on the discovery of nova shells surrounding the post-nova systems V4362 Sagittarii (1994) and more limited observations of DO Aquilae (1925). Distance measurements of 0.5+1.4 -0.2 kpc for V4362 Sgr and 6.7 +/- 3.5 kpc for DO Aql are found based on the expansion parallax method. The growth rates are measured to be 0.07 arcsec yr-1 for DO Aql and 0.32 arcsec yr-1 for V4362 Sgr. A preliminary investigation into the ionization structure of the nova shell associated with V4362 Sgr is presented. The observed ionization structure of nova shells depends strongly on their morphology and the orientation of the central component towards the observer. X-ray, IR, and UV observations as well as optical integral field unit spectroscopy are required to better understand these interesting objects

Deep optical study of the mixed-morphology supernova remnant G 132.7+1.3 (HB3)

We present optical CCD images of the large supernova remnant (SNR) G 132.7+1.3 (HB3) covering its full extent for the first time, in the emission lines of Hα +[N II], [S II], and [O III], where new and known filamentary and diffuse structures are detected. These observations are supplemented by new low-resolution long-slit spectra and higher resolution images in the same emission lines. Both the flux-calibrated images and spectra confirm that the optical emission originates from shock-heated gas since the [S II]/Hα > 0.4. Our findings are also consistent with the recently developed emission-line ratio diagnostics for distinguishing SNRs from H II regions. A multiwavelength comparison among our optical data and relevant observations in radio, X-rays, gamma-rays and CO bands, provided additional evidence on the interaction of HB3 with the surrounding clouds and clarified the borders of the SNR and the adjacent cloud. We discuss the supernova (SN) properties and evolution that led to the current observables of HB3 and we show that the remnant has most likely passed at the pressure driven snowplow phase. The estimated SN energy was found to be (3.7 ± 1.5) × 1051 erg and the current SNR age (5.1 ± 2.1) × 104 yr. We present an alternative scenario according to which the SNR evolved in the wind bubble cavity excavated by the progenitor star and currently is interacting with its density walls. We show that the overall mixed morphology properties of HB3 can be explained if the SN resulted by a Wolf−Rayet progenitor star with mass ∼34 M⊙⁠

High-velocity string of knots in the outburst of the planetary nebula Hb4

The bipolar collimated outflows of the Hb4 planetary nebula (PN) exhibit an evident decrease in their expansion velocity with respect to the distance from the central star. So far, similar velocity law has also been found in Herbig-Haro objects. The interpretation of this peculiar velocity law and the classification of the outflows is the main focal point of this paper. High-dispersion long-slit echelle spectra along with high-resolution images from the Hubble Space Telescope (HST) are applied in the astronomical code shape in order to reproduce a three-dimensional morpho-kinematical model for the core and the bipolar outflows. Its central part shows a number of low-ionization filamentary structures (knots and jets) indicative of common-envelope PN evolution and it is reconstructed assuming a toroidal structure. The high-resolution HST [N ii] image of Hb4 unveils the fragmented structure of outflows. The northern and southern outflows are composed of four and three knots, respectively, and each knot moves outwards with its own expansion velocity. These are reconstructed as a string of knots rather than jets.This string of knots is formed by ejection events repeated every 200-250 yr. Hb4 displays indirect evidence of a binary central system with a Wolf-Rayet companion evolved through the common envelopes channel. The observed deceleration of the knots is likely to be associated with shock collisions between the knots and the interstellar medium or nebular material. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

First 3D morpho-kinematic model of supernova remnants. The case of VRO 42.05.01 (G166.0+4.3)

We present the first three-dimensional (3D) morpho-kinematic (MK) model of a supernova remnant (SNR), using as a case study the Galactic SNR VRO 42.05.01. We employed the astrophysical code SHAPE in which wide field imaging and high-resolution spectroscopic data were utilized, to reconstruct its 3D morphology and kinematics. We found that the remnant consists of three basic distinctive components that we call: a 'shell', a 'wing', and a 'hat'. With respect to their kinematical behaviour, we found that the 'wing' and the 'shell' have similar expansion velocities (Vexp = 115 ± 5 km s-1). The 'hat' presents the lowest expansion velocity of the remnant (Vexp = 90 ± 20 km s-1), while the upper part of the 'shell' presents the highest velocity with respect to the rest of the remnant (Vexp = 155 ± 15 km s-1). Furthermore, the whole nebula has an inclination of ∼3°-5° with respect to the plane of the sky and a systemic velocity of Vsys = -17 ± 3 km s-1. We discuss the interpretation of our model results regarding the origin and evolution of the SNR and we suggest that VRO 42.05.01 had an interaction history with an inhomogeneous ambient medium most likely shaped by the mass outflows of its progenitor star. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

Two new nova shells associated with V4362 Sagittarii and DO Aquilae

A classical nova is an eruption on the surface of a white dwarf in an accreting binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell. The shaping mechanisms of nova shells are probes of the processes that take place at energy scales between planetary nebulae and supernova remnants. We report on the discovery of nova shells surrounding the post-nova systems V4362 Sagittarii (1994) and more limited observations of DO Aquilae (1925). Distance measurements of 0.5+1.4-0.2 kpc for V4362 Sgr and 6.7 ± 3.5 kpc for DO Aql are found based on the expansion parallax method. The growth rates are measured to be 0.07 arcsec yr-1 for DO Aql and 0.32 arcsec yr-1 for V4362 Sgr. A preliminary investigation into the ionization structure of the nova shell associated with V4362 Sgr is presented. The observed ionization structure of nova shells depends strongly on their morphology and the orientation of the central component towards the observer. X-ray, IR, and UV observations as well as optical integral field unit spectroscopy are required to better understand these interesting objects. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

Deep optical study of the mixed-morphology supernova remnant G 132.7+1.3 (HB3)

We present optical CCD images of the large supernova remnant (SNR) G 132.7+1.3 (HB3) covering its full extent for the first time, in the emission lines of Hα +[N ii], [S ii], and [O iii], where new and known filamentary and diffuse structures are detected. These observations are supplemented by new low-resolution long-slit spectra and higher resolution images in the same emission lines. Both the flux-calibrated images and spectra confirm that the optical emission originates from shock-heated gas since the [S ii]/Hα > 0.4. Our findings are also consistent with the recently developed emission-line ratio diagnostics for distinguishing SNRs from H ii regions. A multiwavelength comparison among our optical data and relevant observations in radio, X-rays, gamma-rays and CO bands, provided additional evidence on the interaction of HB3 with the surrounding clouds and clarified the borders of the SNR and the adjacent cloud. We discuss the supernova (SN) properties and evolution that led to the current observables of HB3 and we show that the remnant has most likely passed at the pressure driven snowplow phase. The estimated SN energy was found to be (3.7 ± 1.5) × 1051 erg and the current SNR age (5.1 ± 2.1) × 104 yr. We present an alternative scenario according to which the SNR evolved in the wind bubble cavity excavated by the progenitor star and currently is interacting with its density walls. We show that the overall mixed morphology properties of HB3 can be explained if the SN resulted by a Wolf-Rayet progenitor star with mass ∼34\rm ∼M. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society

Comparative performance of selected variability detection techniques in photometric time series data

Photometric measurements are prone to systematic errors presenting a challenge to lowamplitude variability detection. In search for a general-purpose variability detection technique able to recover a broad range of variability types including currently unknown ones, we test 18 statistical characteristics quantifying scatter and/or correlation between brightness measurements. We compare their performance in identifying variable objects in seven time series data sets obtained with telescopes ranging in size from a telephoto lens to 1 m-class and probing variability on time-scales from minutes to decades. The test data sets together include light curves of 127 539 objects, among them 1251 variable stars of various types and represent a range of observing conditions often found in ground-based variability surveys. The real data are complemented by simulations. We propose a combination of two indices that together recover a broad range of variability types from photometric data characterized by a wide variety of sampling patterns, photometric accuracies and percentages of outlier measurements. The first index is the interquartile range (IQR) of magnitude measurements, sensitive to variability irrespective of a time-scale and resistant to outliers. It can be complemented by the ratio of the light-curve variance to the mean square successive difference, 1/η, which is efficient in detecting variability on time-scales longer than the typical time interval between observations. Variable objects have larger 1/η and/or IQR values than non-variable objects of similar brightness. Another approach to variability detection is to combine many variability indices using principal component analysis.We present 124 previously unknown variable stars found in the test data. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society