We present observations of SN 2023xgo, a transitional Type Ibn/Icn SN, from-5.6 to 63 d relative to r-band peak. Early spectra show C III lambda 5696 emission like Type Icn SNe, shifting to Type Ibn features. The He I velocities (1800-10 000 km s(-1)) and pseudo-equivalent widths are among the highest in the Ibn/Icn class. The light curve declines at 0.14 mag d(-1) until 30 d, matching SNe Ibn/Icn but slower than fast transients. SN 2023xgo is the faintest in our SN Ibn sample ( M-r = -17.65 +/- 0 . 04) but shows typical colour and host properties. Semi-analytical modelling of the light curve suggests a compact CSM shell (similar to 10(12)-10(13) cm), mass-loss rate between 10(-4) and 10(-3) M-circle dot yr(-1) with CSM and ejecta masses of similar to 0.22 and 0.12 M-circle dot, respectively. Post-maximum light-curve, spectral modelling favours a similar to 3 M-circle dot helium star progenitor with extended (similar to 10(15) cm), stratified CSM (density exponent of 2.9) and mass-loss rate of 0 . 1-2 . 7 M-circle dot yr(-1). These two mass-loss regimes imply a radially varying CSM, shaped by asymmetry or changes in the progenitor's mass-loss over time. This mass-loss behaviour fits both binary and single-star evolution. Early Icn-like features stem from hot carbon ionization, fading to Ibn-like with cooling. SN 2023xgo thus offers rare insight into the connection between SNe Icn, Ibn, and SNe Ibn with ejecta signatures.

We present extensive ultraviolet to optical photometric and optical to near-infrared (NIR) spectroscopic follow-up observations of the nearby intermediate-luminosity (MV = -16.81 +/- 0.19 mag) Type Iax supernovae (SNe Iax) 2024pxl in NGC 6384. SN 2024pxl exhibits a faster light curve than the high-luminosity members of this class, and slower than low-luminosity events. The observationally well-constrained rise time of similar to 11 days and an estimated synthesized 56Ni mass of 0.03 M circle dot, based on analytical modeling of the integrated spectral energy distribution light curve, are consistent with models of the weak deflagration of a carbon-oxygen white dwarf. Our optical spectral sequence of SN 2024pxl shows weak Si ii lines and spectral evolution similar to other high-luminosity SNe Iax, but also a prominent early-time C ii line, like lower-luminosity SNe Iax. The late-time optical spectrum of SN 2024pxl closely matches that of SN 2014dt, and its NIR spectral evolution aligns with that of other well-studied, high-luminosity SNe Iax. The spectral-line expansion velocities of SN 2024pxl are at the lower end of the SNe Iax velocity distribution, and the velocity distribution of iron-group elements compared to intermediate-mass elements suggests that the ejecta are mixed on large scales, as expected in pure deflagration models. SN 2024pxl exhibits characteristics intermediate between those of high-luminosity and low-luminosity SNe Iax, further establishing a link across this diverse class.

We present comprehensive photometric and spectroscopic observations of SN 2022eyw, a luminous member of the Type Iax supernova (SN Iax) subclass. SN 2022eyw reached a peak absolute magnitude of M _g = –17.80 ± 0.15 mag and exhibited a rise time of ∼15 days, placing it among the brighter Iax events. The bolometric light curve indicates a synthesized ^56 Ni mass of 0.11 ± 0.01 M _⊙ , with an estimated ejecta mass of 0.79 ± 0.09 M _⊙ and kinetic energy of 0.19 × 10 ^51 erg. The spectral evolution from −8 to +110 days past maximum reveals features characteristic of bright SNe Iax, including a transition from Fe iii to Fe ii dominance, moderate expansion velocities, and a lack of strong C ii absorption. TARDIS spectral modeling of the early-phase spectra indicates well-mixed ejecta dominated by Fe-group elements. In addition, traces of unburnt carbon are detected, pointing to incomplete burning as expected in pure deflagration models. The late-time spectral evolution shows a blend of permitted and forbidden lines. Comparison with deflagration models suggests that SN 2022eyw originated from a partial deflagration of a Chandrasekhar-mass white dwarf, with explosion properties intermediate between the N3-def and N5-def models. These observations support pure deflagration of a CO white dwarf as a viable explosion mechanism for its luminous members.

Accretion-driven outbursts in young stellar objects remain poorly understood, largely limited by a statistically small sample of closely followed-up events. This underscores the importance of a thorough exploration of each outbursting object. We studied a peculiar outbursting system, Gaia24ccy, which exhibited two Delta g similar to 3.8 mag outbursts in 2019 and 2024. The system consists of two unresolved, nearly identical, and rapidly rotating young stars: Gaia24ccy A (1.1419 days) and Gaia24ccy B (1.7898 days). Periodogram analyses just before the onset of the outbursts suggest Gaia24ccy B to be the outbursting component. Unlike any previously known EXor sources, the two outburst profiles show very similar evolution: both rose at the same rate for the first 15 days, followed by multiple "subbursts" on timescales of 10-20 days. The 2019 outburst lasted 145-255 days, while the 2024 outburst persisted for 367 days. We infer the unstable region to lie at rtrigger similar or equal to 0.019-0.047 au (similar to 5-12.3R star). The accreted mass per event, Macc similar to 10-5 M circle dot, can be provided by a compact inner-disk reservoir. The photometric rise and decay timescales, together with the mid-infrared (MIR) color evolution, favor a thermal-viscous trigger in a hot inner disk, while the presence of rich emission-line spectra indicates concurrent magnetospheric compression-together forming a hybrid picture. Finally, we explain the reddening of the MIR color observed during the outburst as a consequence of the competing emission from the viscous disk and the photosphere.

We present photometric and spectroscopic studies of two core-collapse supernovae (SNe) 2008aq and 2019gaf in the optical wavelengths. Light curve and spectral sequence of both the SNe are similar to those of other Type IIb SNe. The pre-maximum spectrum of SN 2008aq showed prominent H alpha lines, the He lines started appearing in the near maximum spectrum. The near maximum spectrum of SN 2019gaf shows shallow H alpha absorption and He lines with almost similar strength. Both the SNe show transition from hydrogen-dominated spectra to helium-dominated spectra within a month after maximum brightness. The velocity evolution of SN 2008aq matches well with those of other well-studied Type IIb SNe, while SN 2019gaf shows higher velocities. Close to maximum light, the H alpha and He i line velocities of SN 2019gaf are similar to 2000 and similar to 4000 km s(-1) higher than other well-studied Type IIb SNe. Semi-analytical modelling indicates SN 2019gaf to be a more energetic explosion with a smaller ejecta mass than SN 2008aq. The zero-age main-sequence (ZAMS) mass of the progenitor estimated using the nebular spectra of SN 2008aq ranges between 13 and 20 M-circle dot, while for SN 2019gaf, the inferred ZAMS mass is between 13 and 25 M-circle dot. The [O I] to [Ca II ] lines flux ratio favours a less massive progenitor star in a binary system for both the SNe.

Type IIn supernovae (SNe) are a subclass of core-collapse SNe powered by interaction between the ejecta and the dense circumstellar material. Among them, long-lived Type IIn events are characterized by luminous, long-duration light curves with high radiative energy. Several cases of long-lived type IIn SNe exhibit substantial dust emission at late times. However, well-observed examples remain limited, and the details of their dust formation mechanisms remain poorly understood. Here we present photometric and spectroscopic observations of the Type IIn SN 2024dy in ultraviolet, optical, and near-infrared (NIR) wavelength for 500 days. SN 2024dy reached a peak magnitude of M_r=-19.2 mag with a total radiation energy of 1.9×10^50 erg. A NIR excess emerged at late phases, and the spectral energy distribution modeling indicates the presence of carbon dust with temperatures of 1300-1800 K and masses of about 10^-5 M_⊙. The spectra features were typical of long-lived Type IIn SNe. The late time Hα profile exhibits a strong suppression of the red wing, providing evidence for newly formed dust. Our results suggest that the derived dust mass above may be underestimated due to optical depth effects. SN 2024dy provides an important observational case for understanding dust formation in Type IIn SNe.

Comet C/2023 A3 (Tsuchinshan-ATLAS) is a non-periodic dynamically new Oort cloud comet that was discovered independently by Purple Mountain Observatory in China and Asteroid Terrestrial-impact Last Alert System (ATLAS) telescopes in South Africa. The comet passed perihelion at a distance of 0.39 AU on 27 September 2024. It was visible to the naked eye (the brightest since the comet C/1995 O1 (Hale-Bopp)) and was dubbed the great comet of 2024. In this work, we investigate the nature of this comet, which is moving in a hyperbolic orbit (e > 1), by analysing its composition using various observational techniques and tracing its orbital evolution through high-precision N-body simulations.

We present the long-term photometric and spectroscopic analysis of a transitioning SN IIn/Ibn from -10.8 d to 150.7 d post V-band maximum. SN 2021foa shows prominent He i lines comparable in strength to the H alpha line around peak, placing SN 2021foa between the SN IIn and SN Ibn populations. The spectral comparison shows that it resembles the SN IIn population at pre-maximum, becomes intermediate between SNe IIn/Ibn, and at post-maximum matches with SN IIn 1996al. The photometric evolution shows a precursor at -50 d and a light curve shoulder around 17 d. The peak luminosity and colour evolution of SN 2021foa are consistent with most SNe IIn and Ibn in our comparison sample. SN 2021foa shows the unique case of an SN IIn where the narrow P-Cygni in H alpha becomes prominent at 7.2 d. The H alpha profile consists of a narrow (500-1200 km s(-1)) component, intermediate width (3000-8000 km s(-1)) and broad component in absorption. Temporal evolution of the H alpha profile favours a disc-like CSM geometry. Hydrodynamical modelling of the light curve well reproduces a two-component CSM structure with different densities (rho proportional to r(-2)-rho proportional to r(-5)), mass-loss rates (10(-3)-10(-1) M-circle dot yr(-1)) assuming a wind velocity of 1000 km s(-1) and having a CSM mass of 0.18 M-circle dot. The overall evolution indicates that SN 2021foa most likely originated from an LBV star transitioning to a WR star with the mass-loss rate increasing in the period from 5 to 0.5 yr before the explosion or it could be due to a binary interaction.

We present panchromatic optical + near-infrared (NIR) + mid-infrared (MIR) observations of the intermediate-luminosity Type Iax supernova (SN Iax) 2024pxl and the extremely low-luminosity SN Iax 2024vjm. JWST observations provide unprecedented MIR spectroscopy of SN Iax, spanning from +11 to +42 day past maximum light. We detect forbidden emission lines in the MIR at these early times while the optical and NIR are dominated by permitted lines with an absorption component. Panchromatic spectra at early times can thus simultaneously show nebular and photospheric lines, probing both inner and outer layers of the ejecta. We identify spectral lines not seen before in SN Iax, including [Mg ii ] 4.76 μ m, [Mg ii ] 9.71 μ m, [Ne ii ] 12.81 μ m, and isolated O i 2.76 μ m that traces unburned material. Forbidden emission lines of all species are centrally peaked with similar kinematic distributions, indicating that the ejecta are well mixed in both SN 2024pxl and SN 2024vjm, a hallmark of pure deflagration explosion models. Radiative transfer modeling of SN 2024pxl shows good agreement with a weak deflagration of a near-Chandrasekhar-mass white dwarf, but additional IR flux is needed to match the observations, potentially attributable to a surviving remnant. Similarly, we find SN 2024vjm is also best explained by a weak deflagration model, despite the large difference in luminosity between the two supernovae. Future modeling should push to even weaker explosions and include the contribution of a bound remnant. Our observations demonstrate the diagnostic power of panchromatic spectroscopy for unveiling explosion physics in thermonuclear supernovae.

We present the analysis of optical photometric and spectroscopic observations of two non-magnetic cataclysmic variables, namely CRTS J080846.2+313106 and V416 Dra. We find CRTS J080846.2+313106 to vary with a period of 4.9116 +/- 0.0003 h, which was not found in earlier studies and which we provisionally suggest is the orbital period of the system. In both long-period systems, the observed dominant signal at the second harmonic of the orbital frequency and the orbital modulation during quiescence are suggestive of ellipsoidal variation from changing aspects of the secondary, with an additional contribution from the accretion stream or hotspot. However, during the outburst, the hotspot itself is overwhelmed by the increased brightness, which is possibly associated with the accretion disc. The mid-eclipse phase for V416 Dra occurs earlier and the width of the eclipse is greater during outbursts compared to quiescence, suggesting an increased accretion disc radius during outbursts. Furthermore, from our investigation of the accretion disc eclipse in V416 Dra, we find that a total disc eclipse is possible during quiescence, whereas the disc seems to be partially obscured during outbursts, which further signifies that the disc may grow in size as the outburst progresses. The optical spectra of CRTS J080846.2+313106 and V416 Dra are typical of dwarf novae during quiescence, and they both show a significant contribution from the M2-4V secondary. The light curve patterns, orbital periods, and spectra observed in the two systems look remarkably similar, and seem to resemble the characteristics of U Gem-type dwarf novae.

ABSTRACT Observing the vibrational/rotational lines in a comet’s optical spectrum requires high-resolution spectroscopy, as they are otherwise seen as a blended feature. To achieve this, we have obtained medium and high-resolution (R (λ/Δλ) = 30 000 and 60 000) spectra of several comets, including C/2015 V2 (Johnson), 46P/Wirtanen, 41P/Tuttle–Giacobini–Kresák, and 38P/Stephan–Oterma, using the Hanle Echelle Spectrograph (HESP) mounted on the 2-m Himalayan Chandra Telescope (HCT) in India. The spectra effectively cover the wavelength range 3700–10 000 Å, allowing us to probe the various vibrational bands and band sequences to identify the rotational lines in the cometary molecular emission. We were also able to separate the cometary Oxygen lines from the telluric lines and analyse the green-to-red (G/R) forbidden oxygen [O i] ratios in a few comets. For comets C/2015 V2, 46P, and 41P, the computed G/R ratios, 0.04 ± 0.01, 0.04 ± 0.01, and 0.08 ± 0.02, respectively, point to H2O being a major source of Oxygen emissions. Notably, in the second fibre pointing at a location 1000 km away from the photocentre of comet 46P, the G/R ratio reduced by more than half the value observed in the first fibre, indicating the effects of quenching within the inner coma. We also measured the NH2 ortho-to-para ratio of comet 46P to be about 3.41 ± 0.05 and derived an ammonia ratio of 1.21 ± 0.03 corresponding to a spin temperature of ∼26 K. With these, we present the results of the study of four comets from different cometary reservoirs using medium and high-resolution optical spectroscopy, emphasizing the capabilities of the instrument for future cometary studies.

We present optical observations and analysis of a bright type Iax SN~2020udy hosted by NGC 0812. The light curve evolution of SN~2020udy is similar to other bright Iax SNe. Analytical modeling of the quasi bolometric light curves of SN 2020udy suggests that 0.08$\pm$0.01 M$_{\odot}$ of $^{56}$Ni would have been synthesized during the explosion. Spectral features of SN 2020udy are similar to the bright members of type Iax class showing weak Si {\sc II} line. The late-time spectral sequence is mostly dominated by Iron Group Elements (IGEs) with broad emission lines. Abundance tomography modeling of the spectral time series of SN~2020udy using TARDIS indicates stratification in the outer ejecta, however, to confirm this, spectral modeling at a very early phase is required. After maximum light, uniform mixing of chemical elements is sufficient to explain the spectral evolution. Unlike the case of normal type Ia SNe, the photospheric approximation remains robust until +100 days, requiring an additional continuum source. Overall, the observational features of SN 2020udy are consistent with the deflagration of a Carbon-Oxygen white dwarf.

We present the optical photometric and spectroscopic analysis of two type Iax SNe 2018cni and 2020kyg. SN 2018cni is a bright type Iax SN (M$_{V,peak}$ = $-$17.81$\pm$0.21 mag) whereas SN 2020kyg (M$_{V,peak}$ = $-$14.52$\pm$0.21 mag) is a faint one. We derive $^{56}$Ni mass of 0.07 and 0.002 M${_\odot}$, ejecta mass of 0.48 and 0.14 M${_\odot}$ for SNe 2018cni and 2020kyg, respectively. A combined study of the bright and faint type Iax SNe in $R/r$- band reveals that the brighter objects tend to have a longer rise time. However, the correlation between the peak luminosity and decline rate shows that bright and faint type Iax SNe exhibit distinct behaviour. Comparison with standard deflagration models suggests that SN 2018cni is consistent with the deflagration of a CO white dwarf whereas the properties of SN 2020kyg can be better explained by the deflagration of a hybrid CONe white dwarf. The spectral features of both the SNe point to the presence of similar chemical species but with different mass fractions. Our spectral modelling indicates stratification at the outer layers and mixed inner ejecta for both the SNe.

LDN1415-IRS, a low-mass young stellar object (YSO), went into an outburst between 2001 and 2006, illuminating a surrounding nebula, LDN1415-Neb. LDN1415-Neb was found to have brightened by I=3.77 mag by April 2006. The optical light curve covering ∼ 15.5 years, starting from October 2006 to January 2022, is presented in this study. The initial optical spectrum indicated the presence of winds in the system, but the subsequent spectra have no wind indicators. The declining light curve and the absence of the P-Cygni profile in later epoch spectra indicate that the star and nebula system is retrieving back from its outburst state. Two Herbig–Haro objects (HHOs) are positioned linearly with respect to the optical brightness peak of the nebula, probably indicating the circumstellar disk being viewed edge-on. Our recent deep near-infrared (NIR) imaging using TANSPEC has revealed the presence of a nearby star-like source, south of the LDN1415-IRS, at an angular distance of ∼5.4” .

Comet 156P/Russell-LINEAR is a short period Jupiter family comet with an orbital period of 6.44 years. The results from spectroscopic, photometric, polarimetric observations and dust modelling studies are presented here. From the spectroscopic study, strong emissions from CN(Δν=0), C3 (λ4050 Å), C2(Δν=+1) and C2(Δν=0) can be observed during both the epochs of our observations. The Q(C2)/Q(CN) ratio classifies the comet as a typical comet. The imaging data reveals the presence of jets. The dust emission from the comet is observed to have a non-steady state outflow due to the presence of these strong jets which subside in later epochs, resulting in a steady state outflow. Polarimetric study at two different phase angles reveals the degree of polarization to be comparable to Jupiter family comets at similar phase angles. Localized variations in polarization values are observed in the coma. The dust modelling studies suggest the presence of high amount of silicate/low absorbing material and indicate the coma to be dominated by higher amount of large size grains with low porosity having power law size distribution index = 2.4. The observed activity and dust properties points to a similarity to another Jupiter family comet, 67P/Churyumov–Gerasimenko.

Manx comets are objects on long-period comet orbits that are inactive as they approach perihelion. They are of particular interest because they may help constrain solar system formation models. 2013 LU28 was discovered as an inactive asteroidal object on 2013 June 8 at a heliocentric distance of 21.8 au. Images and photometric data were obtained of 2013 LU28 from multiple telescopes from pre-discovery data in 2010 until the present. Its spectral reflectivity is consistent with typical organic-rich comet surfaces with colors of g' - r' = 0.97 +/- 0.02, r' - i' = 0.43 +/- 0.02, and r' - z' = 0.65 +/- 0.03, corresponding to a spectral reflectivity slope of 30 +/- 3%/ 100 nm. There is no obvious indication of dust coma in deep stacked images. We estimate the nucleus radius to be similar to 55.7 +/- 0.3 km assuming an albedo of 4%. This is much smaller than the 1 sigma upper limits on the nucleus size of 79.9 km from the NEOWISE survey assuming the same albedo, since the NEOWISE survey is not very sensitive to objects this small at this distance. The heliocentric light curve suggests possible activity between r similar to 17 and 13 au where 2013 LU28 is brighter than expected. This is consistent with outgassing from CO or CO2. Using surface brightness profiles, we estimate an upper limit of X0.01 kg s(-1) for micron-sized dust that can be produced without us detecting it for the inactive portion of the light curve, and upper limits of similar to 1 kg s(-1) for CO and similar to 1.5 kg s(-1) for CO2 between 20 and 14.7 au.

We present optical photometric and spectroscopic analysis of a Type Iax supernova (SN) 2020rea situated at the brighter luminosity end of Type Iax supernovae (SNe). The light curve decline rate of SN~2020rea is $\Delta$m$_{15}$(g) = 1.31$\pm$0.08 mag which is similar to SNe 2012Z and 2005hk. Modelling the pseudo bolometric light curve with a radiation diffusion model yields a mass of $^{56}$Ni of 0.13$\pm$0.01 M$_{\odot}$ and an ejecta mass of 0.77$^{+0.11}_{-0.21}$ M$_{\odot}$. Spectral features of SN~2020rea during the photospheric phase show good resemblance with SN 2012Z. TARDIS modelling of the early spectra of SN~2020rea reveals a dominance of Iron Group Elements (IGEs). The photospheric velocity of the Si {\sc II} line around maximum for SN~2020rea is $\sim$ 6500 km s$^{-1}$ which is less than the measured velocity of the Fe {\sc II} line and indicates significant mixing. The observed physical properties of SN~2020rea match with the predictions of pure deflagration model of a Chandrasekhar mass C-O white dwarf. The metallicity of the host galaxy around the SN region is 12+log(O/H) = 8.56$\pm$0.18 dex which is similar to that of SN 2012Z.

Comet 2I/Borisov is the first true interstellar comet discovered. Here we present results from observational programs at two Indian observatories, 2 m Himalayan Chandra Telescope at the Indian Astronomical Observatory, Hanle (HCT) and 1.2 m telescope at the Mount Abu Infrared Observatory (MIRO). Two epochs of imaging and spectroscopy were carried out at the HCT and three epochs of imaging at MIRO. We found CN to be the dominant molecular emission on both epochs, 31/11/2019 and 22/12/2019, at distances of rH = 2.013 and 2.031 AU respectively. The comet was inferred to be relatively depleted in Carbon bearing molecules on the basis of low C2 and C3 abundances. We find the production rate ratio, Q(C2)/Q(CN) = 0.54 ± 0.18, pre-perihelion and Q(C2)/Q(CN) = 0.34 ± 0.12 post-perihelion. This classifies the comet as being moderately depleted in carbon chain molecules. Using the results from spectroscopic observations, we believe the comet to have a chemically heterogeneous surface having variation in abundance of carbon chain molecules. From imaging observations we infer a dust-to-gas ratio similar to carbon chain depleted comets of the Solar system. We also compute the nucleus size to be in the range 0.18 ≤ r ≤ 3.1 Km. Our observations show that 2I/Borisov’s behaviour is analogous to that of the Solar system comets.

We present comprehensive spectroscopic and photometric analyses of the intermediate luminosity Type Iax supernova (SN Iax) 2019muj based on multi-band datasets observed through the framework of the OISTER target-of-opportunity program. SN 2019muj exhibits almost identical characteristics with the subluminous SNe Iax 2008ha and 2010ae in terms of the observed spectral features and the light curve evolution at the early phase, except for the peak luminosity. The long-term observations unveil the flattening light curves at the late time as seen in a luminous SN Iax 2014dt. This can be explained by the existence of an inner dense and optically-thick component possibly associated with a bound white dwarf remnant left behind the explosion. We demonstrate that the weak deflagration model with a wide range of the explosion parameters can reproduce the late-phase light curves of other SNe Iax. Therefore, we conclude that a common explosion mechanism operates for different subclass SNe Iax.

Light-induced reactions are the first step of many chemical and biological processes like vision and photosynthesis. The timescale of such reactions is of the order of picoseconds to nanoseconds, so studying these ultrafast reactions in real-time requires the use of intense ultrashort lasers having tens of femtoseconds (fs) or shorter pulse duration. In this study, we have used 800 nm, 29 fs, 1 kHz pulses from a Ti:sapphire laser to study the photodissociation of gas-phase CH3OH in a home-built Velocity Map Imaging Spectrometer (VMIS). Strong-field ionization of methanol with the laser pulses results in processes like excitation, ionization, bond-breaking, intramolecular H-atom migration, and bond association, prior to complete molecular fragmentation. Our study focused on the intramolecular H-atom migration in methanol, leading to the formation of Hn+ (n=1-3) ions, and controlling the yield of the Hn + ions using different laser parameters like intensity, pulse duration, wavelength, and polarization. We have confirmed the H2 + and H3 + formation Figure: (left) (a) Schematic diagram of the experimental setup. (b) (I) and (II) show the Hn + (n=1, 2, 3) ions’ VMI images for 800 nm, 29 fs and 195 fs pulses, respectively, (III) shows the time-of-flight (TOF) mass spectrum recorded for methanol, (c) pulse characterization using SPIDER, and (d) multi-plate VMIS. (right) Normalised yield of H2 + and H3 + ions for 800 nm and 1300 nm pulses, plotted as a function of laser intensity. Strong-field ionization of polyatomic molecules