arXiv subjects

Rhorom Priyatikanto

Publications and source records attributed to Rhorom Priyatikanto.

10 recordsLinked to original sources

arXiv2026

Seeing at Timau National Observatory Based on ERA5 Dataset

Understanding the seeing conditions is crucial for astronomical observations using a ground-based telescope. This study analyzes long-term atmospheric data (2002-2021) from the ERA5 dataset to assess the seeing conditions at the new Timau National Observatory in Indonesia, which will house a 3.8-meter optical telescope. While the ERA5 dataset shows good agreement with radiosonde data for temperature and wind speed, it tends to underestimate seeing at Eltari Airport, Kupang. Despite this discrepancy, the ERA5 data suggest a median seeing of 0.79 arcseconds at Timau, with optimal seeing conditions in March and December and greater variability during the May to September dry season. These findings are crucial for the planning and operation of the observatory, which requires excellent seeing conditions for its three-band optical imager and a near-infrared camera. Although the seeing at Timau is not as good as some other observatories, the conditions at Timau make it an observatory that has good prospects for equatorial regions.

astro-ph.IM↗

arXiv2022

Characterisation of Timau National Observatory using limited in-situ measurements

A new astronomical observatory in southeastern Indonesia is currently under construction. This Timau National Observatory will host a 3.8-metre telescope for optical and near-infrared observations. To support the operation and planning, the characterisation of the site needs to be appropriately performed. However, limited resources and access to the site hindered the deployment of instruments for comprehensive site testing. Fortunately, \emph{in-situ} sky brightness data from the Sky Quality Meter (SQM) have been available for almost two years. Based on the data acquired in 470 nights, we obtain a background sky brightness of $μ_0=21.86\pm0.38$ magnitude/arcsec$^2$. Additionally, we evaluate the moonlit sky brightness to estimate the atmospheric extinction coefficient ($k$) and level of scattering on site. We find an alleviated value of $k=0.48\pm0.04$, associated with a high atmospheric aerosol content. It is considered regular for an equatorial area situated at a low altitude (${\sim}1300$ masl). By analysing the fluctuation of the sky brightness and infrared images from \emph{Himawari-8} satellite, we estimate the available observing time (AOT) of at least $5.3$ hours/night and the yearly average percentage of usable nights of $66\%$. The monthly average AOT from SQM and satellite data analysis correlate with $R=0.82$. In terms of the monthly percentage of usable nights, the correlation coefficient is $R=0.78$. During the wet season (November-April), the results from SQM and satellite data analysis deviate more significantly, mainly due to the limited capability of Himawari-8 in detecting fragmented low-altitude clouds. According to these results, we expect Timau to complement other observatories greatly.

astro-ph.IM↗

arXiv2022

Searching for white dwarf variables in TESS data

A sample of 4 thousands Gaia sources with apparent $G$-band magnitudes of $<17$ and trigonometric parallaxes of $>3.33$ milli-arcseconds were cross-matched to the Transiting Exoplanet Survey high level science products and the Full-Frame Images in order to extract the light curves of possible white dwarf variables. Most of the targets in the sample were observed in at least 27-day observing cycle with 30-minutes cadence. Based on Lomb-Scargle periodogram constructed from de-trended light curves, more than 600 sources have indication of periodic variability. This paper presents the early results from the identification.

astro-ph.SR↗

arXiv2016

Ludendorff Coronal Flattening Index of the Total Solar Eclipse on March 9, 2016

Ludendorff coronal flattening index of the Total Solar Eclipse (TSE) on March 9, 2016, was calculated at various distances in solar radius. As a result, we obtained the coronal flattening index $\left(ε=a+b\right)$ at a distance of 2 solar radii is 0.16. The $24^{th}$ solar cycle phase based on the 2016 TSE event obtained -0.64 which showed the corona is pre-minimum type. Resulted coronal flattening index value gives a predicted maximum amplitude of the monthly sunspot number ($W_{max}$) for the $25^{th}$ solar cycle to be $70\pm65$. Therefore, the solar activity for $25^{th}$ solar cycle predicted to be lower than the current solar cycle, which has a maximum sunspot number value of 146 in February 2014

astro-ph.SR↗

arXiv2016

Shape Parameters of 1991 to 2016 Solar Corona

The global structure of solar corona observed in optical window is governed by the global magnetic field with different characteristics over solar activity cycle. Ludendorff flattening index becomes a popular measure of the global structure of solar corona as observed during eclipse. In this study, 15 digital images of solar corona from 1991 to 2016 were analyzed in order to construct the coronal flattening profiles as a function of radius. In most of the cases, the profile can be modeled with 2nd order polynomial function so that the radius with maximum flattening index ($R_{\text{max}}$) can be determined. Along with this value, Ludendorff index ($a+b$) was also calculated. Both Ludendorff index and $R_{\text{max}}$ show anti-correlation with monthly sunspot number, though the $R_{\text{max}}$ values are more scattered. The variation of $R_{\text{max}}$ can be regarded as the impact of changing coronal brightness profile over equator.

astro-ph.SR↗

arXiv2014

Moreton Waves Related to the Flare Event in 3 June 2012 and 6 July 2012

In this study, we present geometrical and kinematical analysis of Moreton wave observed in 2012 June 3rd and July 6th, recorded in H-$α$ images of Global Oscillation Network Group (GONG) archive. These large-scale waves exhibit different features compared to each other. The observed wave of June 3rd has angular span of about $70^{\circ}$ with a diffuse wave front associated to NOAA active region 11496. It was found that the speed of the wave that started propagating at 17.53 UT is about $931\pm80$ km/s. The broadness nature of this Moreton wave can be interpreted as the vertical extension of the wave over the chromosphere. On the other hand, the wave of July 6th may be associated to X1.1 class flare that occurred at 23.01 UT around the 11515 active region. From the kinematical analysis, the wave propagated with the initial velocity of about $994\pm70$ km/s which is in agreement with coronal shock velocity derived from type II radio burst observation, $v\sim1100$ km/s. These two identified waves add the inventory of the large-scale waves observed in 24th Solar Cycle.

astro-ph.SR↗

arXiv2013

On the Evolution of BM Orionis

BM Orionis, eclipsing binary system that located in the center of Orion Nebula Cluster posses several enigmatic problems. Its intrinsic nature and nebular environment make it harder to measure the physical parameters of the system, but it is believed as Algol type binary where secondary component is pre-main sequence star with larger radius. To assure this, several stellar models ($M_1=5.9$ {M_{\odot}} and $M_2=2.0$ {M_{\odot}}) are created and simulated using MESA. Models with rigid rotation of $ω=10^{-5}$ rad/s exhibit considerable similar properties during pre-main sequence stage, but 2.0 {\msun} at assumed age of $\sim10^6$ is $6.46$ times dimmer than observed secondary star. There must be an external mechanism to fill this luminosity gap. Then, simulated post-main sequence binary evolution of BM Ori that involves mass transfer shows that primary star will reach helium sequence with the mass of $\sim0.8$ {\msun} before second stage mass transfer.

astro-ph.SR↗

arXiv2013

Suryakala-Nusantara: Documenting Indonesian Sundials

Sundial is the ancient or classic timekeeper device, especially prior to the invention of mechanical clock. In the classical Islamic civilization, the daily movement of the Sun becomes main indicator of praying time, which can be deduced using sundial. This kind of device probably permeated to Indonesia during the Islamic acculturation. Since then, the development of astronomical knowledge, technology, art and architectural in classical Indonesia are partially reflected into sundial. These historical attractions of sundial demand comprehensive documentation and investigation of Indonesian sundial which are rarely found in the current literatures. The required spatial and temporal information regarding Indonesian sundial can be collected by general public through citizen science scheme. This concept may answer scientific curiosity of a research and also educate the people, expose them with science. In this article, general scheme of citizen science are discussed, its application for sundial study in Indonesia is proposed as Suryakala-Nusantara program.

physics.pop-ph↗

arXiv2013

On The Period Determination of ASAS Eclipsing Binaries

Variable stars, or particularly eclipsing binaries, are very essential astronomical occurrence. Surveys are the backbone of astronomy, and many discoveries of variable stars are the results of surveys. All-Sky Automated Survey (ASAS) is one of the observing projects whose ultimate goal is photometric monitoring of variable stars. Since its first light in 1997, ASAS has collected 50,099 variable stars, with 11,076 eclipsing binaries among them. In the present work we focus on the period determination of the eclipsing binaries. Since the number of data points in each ASAS eclipsing binary light curve is sparse, period determination of any system is a not straightforward process. For 30 samples of such systems we compare the implementation of Lomb-Scargle algorithm which is an Fast Fourier Transform (FFT) basis and Phase Dispersion Minimization (PDM) method which is non-FFT basis to determine their period. It is demonstrated that PDM gives better performance at handling eclipsing detached (ED) systems whose variability are non-sinusoidal. More over, using semi-automatic recipes, we get better period solution and satisfactorily improve 53% of the selected object's light curves, but failed against another 7% of selected objects. In addition, we also highlight 4 interesting objects for further investigation.

astro-ph.SR↗

arXiv2013

Open Cluster Evolutions in Binary System: How They Dissolved

Binarity among stellar clusters in galaxy is such a reality which has been realized for a long time, but still hides several questions and problems to be solved. Some of binary star clusters are formed by close encounter, but the others are formed together from similar womb. Some of them undergo separation process, while the others are in the middle of merger toward common future. The products of merger binary star cluster have typical characteristics which differ from solo clusters, especially in their spatial distribution and their stellar members kinematics. On the other hand, these merger products still have to face dissolving processes triggered by both internal and external factors. In this study, we performed N-body simulations of merger binary clusters with different initial conditions. After merging, these clusters dissolve with greater mass-loss rate because of their angular momentum. These rotating clusters also experience more deceleration caused by external tidal field.

astro-ph.GA↗