arXiv subjects

Puji Irawati

Publications and source records attributed to Puji Irawati.

14 recordsLinked to original sources

arXiv2026

First and Comprehensive Study of V0757 Pup : $\gamma-$Doradus Pulsator in Detached Eclipsing Binary

Pulsating stars in detached eclipsing binary (EA) systems are known for providing many important physical informations which constrain both stellar structure and evolution theories. To date, fewer than 50 $\gamma$ Doradus (GDOR) stars have been found in eclipsing binary systems, making them important targets to study \textit{g}-mode pulsation inside the stars. We present a comprehensive physical and pulsational analysis of V0757 Pup (TIC 6939791), a detached eclipsing binary system observed by the TESS mission (Sectors 7, 34, 61, and 88) and followed up with ground-based spectroscopy from the Thai National Telescope. By combining light curve modeling with radial velocities derived from medium-resolution spectra, we determined the fundamental stellar and atmospheric parameters with high precision. The system consists of an F2V primary ($M_1=1.305\pm0.026M_\odot, R_1=1.643\pm0.020R_\odot$) and a G1V secondary ($M_2=0.934\pm0.030M_\odot, R_2=0.941\pm0.079R_\odot$). We performed a detailed frequency analysis of the residual light curves, identifying two dominant independent pulsation frequencies at $f\sim0.79$ c/d and $0.98$ c/d. These frequencies, along with the derived pulsation constant ($Q\sim0.6$ d), confirm the primary component as a $\gamma$ Doradus pulsator. An analysis of Eclipse Timing Variations (ETV) reveals non detection of third body companions with current available dataset, strengthen by the result of \textit{Gaia} astrometric analysis. Evolutionary modeling indicates the system is $\sim2.2$ Gyr old, with the primary expected to fill its Roche lobe in $\sim1$ Gyr. Additionally, we calculate a distance of $d\approx350$ pc based on orbital and SED modeling, which is in excellent agreement with the \textit{Gaia} DR3 parallax distance.

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arXiv2025

Further evidence for natal kick segregation by spectral type in high-mass X-ray binaries

High-mass X-ray binaries (HMXBs) are systems in which a neutron star or black hole accretes material from a massive companion. HMXBs are expected to have experienced a supernova in their evolution. The impulsive kick associated with this event should affect the space velocity of the system in a way that depends on the nature and state of the progenitor binary. Here, we test whether the different evolutionary histories of HMXBs have left a detectable imprint on their peculiar velocities ($V_{\rm pec}$). Using data from Gaia Data Release 3 (Gaia DR3), we first calculate the $V_{\rm pec}$ values for 63 well-known HMXBs hosting a black hole or neutron star and estimate the associated uncertainties via Monte Carlo re-sampling. We then analyse their distribution and check for differences between classes. Overall, $V_{\rm pec}$ estimates extend up to 100 km s$^{-1}$, but with Be/X-ray binaries (BeXRBs) favouring $V_{\rm pec}$ $\lesssim 40$ km s$^{-1}$ and supergiant X-ray binaries (SgXRBs) favouring $V_{\rm pec}$ $\gtrsim 40$ km s$^{-1}$. Based on a Kolmogorov-Smirnov (K-S) test, the null hypothesis that the peculiar velocities of both classes are drawn from the same parent distribution can be robustly rejected, irrespective of the background stellar velocity dispersion. Tests with binary population synthesis demonstrate that SgXRBs typically have shorter orbital periods and higher fractional mass loss than BeXRBs at supernova. We argue that the magnitude of $V_{\rm pec}$ could be used as a complementary feature to distinguish between Be and supergiant systems. These findings extend previous inferences based on two-dimensional kinematics from Hipparcos, and may be explained by the differing nature of the respective progenitors systems between the source classes at the instant of supernova.

astro-ph.HE↗

arXiv2025

Characterisation of H$\beta$ spectra from EXO 051910+3737.7 X-rays binaries

We investigate the spectral characteristics of the Be/X-ray binary system, EXO 051910+3737.7, in which Be/X-ray systems are the largest sub-class of high-mass X-ray binaries. Spectroscopic observations are taken by the Thai National Telescope (TNT) with a Medium-RESolution spectrograph (MRES) instrument for seven nights spanning from 2020 to 2021. Our primary focus is directed towards the analysis of two Balmer lines, namely H$\alpha$ and H$\beta$, given that Be stars typically exhibit emission features in at least one of these hydrogen Balmer lines during certain phases. Our observations reveal split Balmer emission lines throughout the entire duration of our monitoring. Double Gaussian profiles were employed for line fitting to characterize these lines. The presence of double peaks in the Balmer lines indicates the presence of asymmetries within the circumstellar disc. We then analyze V/R variations and the changes in H$\beta$ spectra. Our analysis of V/R variation which Violet (V) and Red (R) peak intensity components, revealed rapid fluctuations occurring within a single day, although determining the precise periodicity was constrained by instrumental limitations and the duration of observability. Furthermore, employing observed the wavelength differences ($\Delta\lambda$) in conjunction with typical Be star parameters allowed us to estimate the radius ($r_{\beta}$) of the H$\beta$ emitting envelope. The average value was calculated to be 2.585$r_*$, with a standard deviation of 0.050$r_*$.

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arXiv2024

Workforce Development in Astronomy and Astroinformatics

Policy Brief on "Workforce Development in Astronomy and Astroinformatics", distilled from the corresponding panel that was part of the discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. The discipline of astronomy and astroinformatics is dynamically evolving thereby creating a compelling opportunity to foster a more inclusive, diverse, and proficient workforce. This is crucial for addressing multifaceted challenges that emerge as we progress and harness the potential therein. To realize this goal, it's imperative to cultivate strategies that promote inclusive practices in STEM education, encourage participation from historically excluded groups, provide training and mentorship, as well as provide active champions, especially for students and early career professionals from (historically) excluded groups. We provide an overview of the current status, resources available, and possible steps especially keeping in mind large international projects. The policy webinar took place during the G20 presidency in India (2023). A summary based on the seven panels can be found here: arxiv:2401.04623.

astro-ph.IM↗

arXiv2024

J0526+5934: a peculiar ultra-short period double white dwarf

Ultra-short period compact binaries are important sources of gravitational waves, which include e.g. the progenitors of type Ia supernovae or the progenitors of merger episodes that may lead to massive and magnetic single white dwarfs. J0526+5934 is an unresolved compact binary star with an orbital period of 20.5 minutes that belongs to this category. The visible component of J0526+5934 has been recently claimed to be a hot sub-dwarf star with a CO white dwarf companion. Our aim is to provide strong observational plus theoretical evidence that the primary star is rather an extremely-low mass white dwarf, although the hot subdwarf nature cannot be completely ruled out. We analyse optical spectra together with time-series photometry of the visible component of J0526+5934 to constrain its orbital and stellar parameters. We also employ evolutionary sequences for low-mass white dwarfs to derive independent values of the primary mass. From the analysis of our observational data, we find a stellar mass for the primary star in J0526+5934 of 0.26+-0.05 Msun, which perfectly matches the 0.237+-0.035 Msun independent measurement we derived from the theoretical evolutionary models. This value is considerably lower than the theoretically expected and generally observed mass range of hot subdwarf stars, but falls well within the mass limit values of extremely low-mass white dwarfs. We conclude J0526+5934 is the fifth ultra-short period detached double white dwarf currently known.

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arXiv2024

AstroInformatics: Recommendations for Global Cooperation

Policy Brief on "AstroInformatics, Recommendations for Global Collaboration", distilled from panel discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. The deliberations encompassed a wide array of topics, including broad astroinformatics, sky surveys, large-scale international initiatives, global data repositories, space-related data, regional and international collaborative efforts, as well as workforce development within the field. These discussions comprehensively addressed the current status, notable achievements, and the manifold challenges that the field of astroinformatics currently confronts. The G20 nations present a unique opportunity due to their abundant human and technological capabilities, coupled with their widespread geographical representation. Leveraging these strengths, significant strides can be made in various domains. These include, but are not limited to, the advancement of STEM education and workforce development, the promotion of equitable resource utilization, and contributions to fields such as Earth Science and Climate Science. We present a concise overview, followed by specific recommendations that pertain to both ground-based and space data initiatives. Our team remains readily available to furnish further elaboration on any of these proposals as required. Furthermore, we anticipate further engagement during the upcoming G20 presidencies in Brazil (2024) and South Africa (2025) to ensure the continued discussion and realization of these objectives. The policy webinar took place during the G20 presidency in India (2023). Notes based on the seven panels will be separately published.

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arXiv2023

Post-outburst evolution of bonafide FUor V2493 Cyg: A Spectro-photometric monitoring

We present here the results of eight years of our near-simultaneous optical/near-infrared spectro-photometric monitoring of bonafide FUor candidate `V2493 Cyg' starting from 2013 September to 2021 June. During our optical monitoring period (between October 16, 2015 and December 30, 2019), the V2493 Cyg is slowly dimming with an average dimming rate of $\sim$26.6 $\pm$ 5.6 mmag/yr in V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing towards a gradual expansion of the emitting region post the second outburst. The mid infra-red colors, on the contrary, exhibits a blueing trend which can be attributed to the brightening of the disc due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the H$\alpha$ line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca II infra-red triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilised compared to the early days of the outburst. The evolution of the O I $\lambda$7773 \AA~ line also points towards the stabilization of the circumstellar disc post the second outburst.

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arXiv2022

Doubling of minute-long Quasi-Periodic Pulsations from super-flares on a low mass star

Using the ULTRASPEC instrument mounted on the 2.4-m Thai National Telescope, we observed two large flares, each with a total energy close to 10^34 erg with sub-second cadence. A combination of a wavelet analysis, a Fourier transform plus an empirical mode decomposition, reveals quasi-period pulsations (QPP) which exhibit an apparent doubling of the oscillation period. Both events showed oscillations of a few minutes over a interval of several minutes, and despite the availability of sub-second cadence, there was no evidence of sub-minute oscillations. The doubling of the QPP periods and shorter lifetime of shorter-period QPP modes strongly favour resonant dynamics of magnetohydrodynamic waves in a coronal loop. We estimate loop lengths to be 0.2-0.7 R*, in agreement with a typical length of solar coronal loops. These observations presents rare and compelling evidence for the presence of compact plasma loops in a stellar corona.

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arXiv2020

An extremely hot white dwarf with a rapidly rotating K-type subgiant companion: UCAC2 46706450

UCAC2 46706450 is a late-type star with an ultraviolet (UV) excess. It was considered a candidate to establish a sample of FGK stars with white dwarf (WD) companions that can be used to test binary evolution models. To verify the WD nature of the companion, UV spectroscopy was performed by Parsons et al. (2016). By a detailed model-atmosphere analysis we show that the UV source is an extremely hot WD with effective temperature $T_\mathrm{eff}$ = $105\,000\pm5000$ K, mass $M/M_\odot = 0.54\pm0.02$, radius $R/R_\odot = 0.040^{+0.005}_{-0.004}$, and luminosity $L/L_\odot= 176^{+55}_{-49}$, i.e., the compact object is just about to enter the WD cooling sequence. Investigating spectra of the cool star ($T_\mathrm{eff}$ = $4945\pm250$ K) we found that it is a K-type subgiant with $M/M_\odot = 0.8-2.4$, $R/R_\odot = 5.9^{+0.7}_{-0.5}$, and $L/L_\odot= 19^{+5}_{-5}$, that is rapidly rotating with $v \sin(i)=81$ km s$^{-1}$. Optical light curves reveal a period of two days and an o-band peak-to-peak amplitude of 0.06 mag. We suggest, that it is caused by stellar rotation in connection with star spots. With the radius we infer an extremely high rotational velocity of $v_{\mathrm{rot}}=151^{+18}_{-13}$ km s$^{-1}$, thus marking the star as one of the most rapidly rotating subgiants known. This explains chromospheric activity observed by H$\alpha$ emission and emission-line cores in CaII H and K as well as NUV flux excess. From equal and constant radial velocities of the WD and the K subgiant as well as from a fit to the spectral energy distribution we infer that they form a physical, wide though unresolved binary system. Both components exhibit similar metal abundances and show iron-group elements with slightly oversolar (up to 0.6 dex) abundance, meaning that atomic diffusion in the WD atmosphere is not yet active due to a residual, weak radiation-driven wind. (abridged)

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arXiv2020

Machine Learning for Transient Recognition in Difference Imaging With Minimum Sampling Effort

The amount of observational data produced by time-domain astronomy is exponentially in-creasing. Human inspection alone is not an effective way to identify genuine transients fromthe data. An automatic real-bogus classifier is needed and machine learning techniques are commonly used to achieve this goal. Building a training set with a sufficiently large number of verified transients is challenging, due to the requirement of human verification. We presentan approach for creating a training set by using all detections in the science images to be thesample of real detections and all detections in the difference images, which are generated by the process of difference imaging to detect transients, to be the samples of bogus detections. This strategy effectively minimizes the labour involved in the data labelling for supervised machine learning methods. We demonstrate the utility of the training set by using it to train several classifiers utilizing as the feature representation the normalized pixel values in 21-by-21pixel stamps centered at the detection position, observed with the Gravitational-wave Optical Transient Observer (GOTO) prototype. The real-bogus classifier trained with this strategy can provide up to 95% prediction accuracy on the real detections at a false alarm rate of 1%.

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arXiv2019

Short period variable stars in young open cluster Stock 8

We present time series photometry in the field of Stock 8 and identified 130 short period variable stars. Twenty eight main-sequence and 23 pre-main-sequence variables are found to be part of cluster Stock 8. The main-sequence variables are classified as slow pulsator of the B type, $\beta$ Cep and $\delta$ Scuti stars. Fourteen main-sequence stars could be new class variables as discussed by Mowlavi et al. (2013) and Lata et al. (2014). The age and mass of pre-main-sequence variables are found to be $\lesssim$ 5 Myr and in the mass range of 0.5 to 2.8 M$_{\odot}$, respectively. These pre-main-sequence stars could be T-Tauri variables. We have found 5 and 2 of 23 PMS variables as classical T-Tauri stars and Herbig Ae/Be stars, respectively, whereas 16 PMS stars are classified as weak-line T Tauri stars.

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arXiv2016

PTF1 J082340.04+081936.5: A hot subdwarf B star with a low mass white dwarf companion in an 87 minute orbit

We present the discovery of the hot subdwarf B star (sdB) binary PTF1 J082340.04+081936.5. The system has an orbital period P$_{\rm orb}=87.49668(1)$ min (0.060761584(10) days), making it the second-most compact sdB binary known. The lightcurve shows ellipsoidal variations. Under the assumption that the sdB primary is synchronized with the orbit, we find a mass $M_{\rm sdB}=0.45^{+0.09}_{-0.07}$ M$_\odot$, a companion white dwarf mass $M_{\rm WD}=0.46^{+0.12}_{-0.09}$ M$_\odot$ and a mass ratio $q = \frac{M_{\rm WD}}{M_{\rm sdB}}=1.03^{+0.10}_{-0.08}$. The future evolution was calculated using the MESA stellar evolution code. Adopting a canonical sdB mass of $M_{\rm sdB}=0.47$ M$_\odot$, we find that the sdB still burns helium at the time it will fill its Roche lobe if the orbital period was less than 106 min at the exit from the last common envelope phase. For longer common envelope exit periods the sdB will have stopped burning helium and turned into a C/O white dwarf at the time of contact. Comparing the spectroscopically derived log(g) and $T_{\rm eff}$ with our MESA models, we find that an sdB model with a hydrogen envelope mass of $5\times10^{-4} M_\odot$ matches the measurements at a post-common envelope age of 94 Myr, corresponding to a post-common envelope orbital period of 109 min which is close to the limit to start accretion while the sdB is still burning helium.

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arXiv2016

Hunting For Eclipses: High Speed Observations of Cataclysmic Variables

We present new time-resolved photometry of 74 cataclysmic variables (CVs), 47 of which are eclipsing. 13 of these eclipsing systems are newly discovered. For all 47 eclipsing systems we show high cadence (1-20 seconds) light curves obtained with the high-speed cameras ultracam and ultraspec. We provide new or refined ephemerides, and supply mid-eclipse times for all observed eclipses. We assess the potential for light curve modelling of all 47 eclipsing systems to determine their system parameters, finding 20 systems which appear to be suitable for future study.

astro-ph.SR↗

arXiv2016

A multiwavelength investigation of the HII region S311: Young stellar population and star formation

We present a multiwavelength investigation of the young stellar population and star formation activities around the \hii region Sharpless 311. Using our deep near-infrared observations and archival {\it Spitzer}-IRAC observations, we have detected a total of 125 young stellar objects (YSOs) in an area of $\sim$86 arcmin$^2$. The YSOs sample include 8 Class I and 117 Class II candidate YSOs. The mass completeness of the identified YSOs sample is estimated to be 1.0 \msun. The ages and masses of the majority of the candidate YSOs are estimated to be in the range of $\sim$0.1$-$5 Myr and $\sim$0.3$-$6 \msun, respectively. The 8 \mum image of S311 displays an approximately spherical cavity around the ionizing source which is possibly created due to the expansion of the \hii region. The spatial distribution of the candidate YSOs reveals that a significant number of them are distributed systematically along the 8 $μ$m emission with a majority clustered around the eastern border of the \hii region. Four clumps/compact \hii regions are detected in the radio continuum observations at 1280 MHz, which might have been formed during the expansion of the \hii region. The estimated dynamical age of the region, main-sequence lifetime of the ionizing source, the spatial distribution and ages of the candidate YSOs indicate triggered star formation in the complex.

astro-ph.GA↗