Vainu Bappu Observatory Research Articles

Impact of Tourism in Economic Development - A Study with Reference to Vellore District

India is widely recognized as one of the most ancient civilizations, characterized by its diverse and culturally significant past. India has long been a focal point of interest for various individuals due to a multitude of factors. India possesses a time-honored heritage of tourism. The industry in question was present within the informal sector since ancient times and was engaged in by individuals from many social groups. India, as an expansive and heterogeneous nation, has something to provide for all individuals. The conventional manner in which visitors are received in India is rooted in the mythological notion of ‘Athithi Devo Bhavah’, which translates to ‘Guest is God’. This is the most recent slogan the Indian tourism sector has used. In order for India to become a global leader in the tourism industry, it is imperative that all branches of the central and state governments, the private sector, and voluntary organizations actively collaborate to achieve sustainable growth in tourism. This is because tourism is a multifaceted activity and primarily a service industry. This study seeks to examine and assess the influence of tourism on the economic progress of Vellore District. This study holds significant importance as a substantial number of individuals visited Vellore, not alone for medical treatment but also for tourism purposes. The prominent tourist destinations in and around Vellore encompass the Historic Vellore Fort, Government Museum, Science Park, Vainu Bappu Observatory, and Amirthi Zoological Park, as well as religious sites such as Jalakandeswarar Temple, Srilakshmi Golden Temple, Big Mosque, St. John’s Church, Yelagiri Hill Station, and CMCH, which offers exceptional medical care at an affordable price.

Decoding the X-Ray Flare from MAXI J0709–159 Using Optical Spectroscopy and Multiepoch Photometry

We present a follow-up study on the recent detection of two X-ray flaring events by MAXI/Gas Slit Camera observations in soft and hard X-rays from MAXI J0709–159 in the direction of HD 54786 (LY CMa), on 2022 January 25. The X-ray luminosity during the flare was around 1037 erg s−1 (MAXI), which got reduced to 1032 erg s−1 (NuSTAR) after the flare. We took low-resolution spectra of HD 54786 from the 2.01 m Himalayan Chandra Telescope and the 2.34 m Vainu Bappu Telescope (VBT) facilities in India, on 2022 February 1 and 2. In addition to Hα emission, we found emission lines of He i in the optical spectrum of this star. By comparing our spectrum of the object with those from the literature we found that He i lines show variability. Using photometric studies we estimate that the star has an effective temperature of 20,000 K. Although HD 54786 is reported as a supergiant in previous studies, our analysis favors it to be evolving off the main sequence in the color–magnitude diagram. We could not detect any infrared excess, ruling out the possibility of IR emission from a dusty circumstellar disk. Our present study suggests that HD 54786 is a Be/X-ray binary system with a compact object companion, possibly a neutron star.

Multiband Transit Follow-up Observations of Five Hot Jupiters with Critical Noise Treatments: Improved Physical Properties

Abstract The most challenging limitation in transit photometry arises from the noises in the photometric signal. In particular, the ground-based telescopes are heavily affected by the noise due to perturbation in the Earth’s atmosphere. Use of telescopes with large apertures can improve the photometric signal-to-noise ratio to a great extent. However, detecting a transit signal out of a noisy light curve of the host star and precisely estimating the transit parameters call for various noise reduction techniques. Here, we present multiband transit photometric follow-up observations of five hot Jupiters e.g., HAT-P-30 b, HAT-P-54 b, WASP-43 b, TrES-3 b, and XO-2 N b, using the 2 m Himalayan Chandra Telescope at the Indian Astronomical Observatory, Hanle, and the 1.3 m J. C. Bhattacharya Telescope at the Vainu Bappu Observatory, Kavalur. Our critical noise treatment approach includes techniques such as wavelet denoising and Gaussian process regression, which effectively reduce both time-correlated and time-uncorrelated noise components from our transit light curves. In addition to these techniques, use of our state-of-the-art model algorithms have allowed us to estimate the physical properties of the target exoplanets with a better accuracy and precision compared to the previous studies.

A near-infrared photometer for the 1-m telescope of Vainu Bappu Observatory

A near-infrared photometer based on an InGaAs PIN photodiode and the filter set recommended by Infrared Working Group (IRWG) have been designed and built. It is mounted on the 1-m Carl–Zeiss telescope at the Vainu Bappu Observatory (VBO) in Kavalur, India. The main science goal is to observe bright sources (< 5 magnitude) in the iZ, iJ and iH photometric bands. A discussion of the instrument and on-telescope performance during first-light tests are presented in this paper.

Helium Enhancement in the Metal-rich Red Giants of ω Centauri

Abstract The helium-enriched (He-enriched) metal-rich red giants of ω Centauri, discovered by Hema &amp; Pandey using the low-resolution spectra from the Vainu Bappu Telescope, and confirmed by the analyses of the high-resolution spectra obtained from the HRS-South African Large Telescope for LEID 34225 and LEID 39048, are reanalyzed here to determine their degree of He enhancement/hydrogen deficiency (H deficiency). The observed MgH band combined with model atmospheres with differing He/H ratios are used for the analyses. The He/H ratios of these two giants are determined by enforcing the fact that the derived Mg abundances from the Mg i lines and from the subordinate lines of the MgH band must be same for the adopted model atmosphere. The estimated He/H ratios for LEID 34225 and LEID 39048 are 0.15 ± 0.04 and 0.20 ± 0.04, respectively, whereas the normal He/H ratio is 0.10. Following the same criteria for the analyses of the other two comparison stars (LEID 61067 and LEID 32169), a normal He/H ratio of 0.10 is obtained. The He/H ratio of 0.15–0.20 corresponds to a mass fraction of helium (Z(He) = Y) of about 0.375–0.445. The range of helium enhancement and the derived metallicity of the program stars are in line with those determined for ω Cen’s blue main-sequence stars. Hence, our study provides the missing link for the evolutionary track of the metal-rich helium-enhanced population of ω Centuari. This research work is the very first spectroscopic determination of the amount of He enhancement in the metal-rich red giants of ω Centauri using the Mg i and MgH lines.

Binary star detection in the open cluster King 1 field

A rarely studied open cluster, King 1 is observed using the 1.3-m telescope equipped with a 2k × 4k CCD at Vainu Bappu Observatory, India. We analyze the photometric data obtained from CCD observations in both B and V bands. Out of 132 detected stars in the open cluster King 1 field, we have identified four stellar variables, and two among them are reported as newly detected binary systems. The parallax values from Gaia DR2 suggest that the open cluster King 1 is in the background of these two detected binary systems, falling along the same line of sight, giving rise to different parallax values. Periodogram analysis was carried out using Phase Dispersion Minimization (PDM) and the Lomb-Scargle (LS) method for all the detected variables. PHysics Of Eclipsing BinariEs (PHOEBE) is extensively employed to model various stellar parameters of both the detected binary systems. Based on the modeling results obtained from this work, one of the binary systems is reported for the first time as an Eclipsing Detached (ED) and the other as an Eclipsing Contact (EC) binary of W-type W UMa.

Development of image motion compensation system for 1.3m telescope at Vainu Bappu Observatory

We developed a tip-tilt system to compensate the turbulence induced image motion for the 1.3 m telescope at Vainu Bappu Observatory, at Kavalur. The instrument is designed to operate at the visible wavelength band (480 − 700 nm) with a field of view of 1′ × 1′. The tilt corrected images have demonstrated up to ≈ 57% improvement in image resolution and a corresponding peak intensity increase by a factor of ≈ 2.8. A closed-loop correction bandwidth of ≈ 26 Hz has been achieved with on-sky tests and the root mean square motion of the star image has been reduced by a factor of ∼ 14. These results are consistent with theoretical and numerical predictions of wave-front aberrations caused by atmospheric turbulence and image quality improvement expected from a real-time control system. In this paper, we present details of the instrument design, laboratory calibration studies and quantify its performance on the telescope.

Precise Photometric Transit Follow-up Observations of Five Close-in Exoplanets: Update on Their Physical Properties

Abstract We report the results of the high-precision photometric follow-up observations of five transiting hot Jupiters, WASP-33b, WASP-50b, WASP-12b, HATS-18b, and HAT-P-36b. The observations are made from the 2 m Himalayan Chandra Telescope at Indian Astronomical Observatory, Hanle, and the 1.3 m J. C. Bhattacharyya Telescope at Vainu Bappu Observatory, Kavalur. This exercise is a part of the capability testing of the two telescopes and their back-end instruments. Leveraging the large aperture of both the telescopes used, the images taken during several nights were used to produce the transit light curves with high photometric signal-to-noise ratio (&gt;200) by performing differential photometry. In order to reduce the fluctuations in the transit light curves due to various sources such as stellar activity, varying sky transparency, etc., we preprocessed them using wavelet denoising and applied a Gaussian process correlated noise modeling technique while modeling the transit light curves. To demonstrate the efficiency of the wavelet denoising process we have also included the results without the denoising process. A state-of-the-art algorithm used for modeling the transit light curves provided the physical parameters of the planets with more precise values than reported earlier.

Estimation and correction of the instrumental perturbations of Vainu Bappu Telescope Echelle spectrograph using a model-based approach

The Echelle spectrograph operating at Vainu Bappu Telescope (VBT), India, is a general purpose instrument used for many high-resolution spectroscopic observations. A concerted effort is being made to expand the scientific capability of the instrument in emerging areas of observational astronomy. The present study is aimed at evaluating the feasibility of the spectrograph to carry out precision Radial Velocity (RV) measurements. In the current design, major factors limiting the RV precision of the spectrograph arise from the movable grating and slit; optical aberrations; positional uncertainty associated with optomechanical mounts and environmental and thermal instabilities in the spectrograph room. RV instabilities due to temperature and pressure variations in the environment are estimated to vary around 120 $ \textrm{ms}^{-1} $ and 400 $ \textrm{ms}^{-1} $ respectively. The positional uncertainty of the grating in the spectrograph could induce a spectral shift $\sim1.4\,\textrm{kms}^{-1} $ across the Echelle orders. A Zemax model is used to overcome the uncertainty in the zero-positioning and lack of repeatability of the moving components. We propose to obtain the ThAr lamp observations and using the Zemax model as the reference, predict the drifts in the positions of the optical components. The perturbations of the optical components from the nominal position are corrected at the beginning of the observational run. After a good match is obtained between the model and the observations, we propose to use a Zemax model to improve the wavelength calibration solution. We could match the observations and model within $\pm$~1 pixels accuracy after the model parameters were perturbed in a real-time setup of the spectrograph. In this paper, we present the estimation of the perturbations of optical components and the effect on the RV obtained.

Toward precision radial velocity measurements using Echelle spectrograph at Vainu Bappu Telescope (Erratum)

The Echelle spectrograph operating at Vainu Bappu Telescope is a general purpose instrument designed for high-resolution spectroscopy. It is being considered for precision Doppler measurements without altering the existing design and basic usage. However, the design level limitations and environmental perturbations are a major source of instability and systematic errors. As a result, a small Doppler signal in the stellar spectra is completely swamped by the large and uncontrolled instrumental drift. We discuss some of the remedial measures we took to improve the radial velocity performance of the spectrograph. We show that an autoguider assembly has greatly reduced the mechanical jitter of the star image at the fiber input, making the illumination of the spectrograph slit at the other end stable. We have also installed an iodine absorption cell to track and eliminate the instrumental drifts to facilitate precision radial velocity observations. Furthermore, we have developed a generic algorithm that uses iodine exposures to extract the stellar radial velocities without the need for the complex forward modeling. Our algorithm is not accurate to the level of traditional iodine technique. However, it is convenient to use on a low-cost general-purpose spectrograph targeting a moderate radial velocity (RV) precision at a few 10 to 100 ms − 1 level. Finally, we have demonstrated the usefulness of our approach by measuring the RV signal of a well-known short-period, planet-hosting star.

Toward precision radial velocity measurements using Echelle spectrograph at Vainu Bappu Telescope

The Echelle spectrograph operating at Vainu Bappu Telescope (VBT) is a general purpose instrument designed for high resolution spectroscopy. It is being considered for precision Doppler measurements without altering the existing design and basic usage. However, the design level limitations and environmental perturbations are a major source of instability and systematic errors. As a result, a small Doppler signal in the stellar spectra is completely swamped by the large and uncontrolled instrumental drift. In this paper, we discuss some of the remedial measures we took to improve the radial velocity performance of the spectrograph. We show that a new auto-guider assembly has greatly reduced the mechanical jitter of the star image at the fibre input, making the illumination of the spectrograph slit at the other end stable. We have also installed an iodine absorption cell to track and eliminate the instrumental drifts to facilitate precision radial velocity observations. Furthermore, we have developed a generic algorithm that uses iodine exposures to extract the stellar radial velocities without the need for the complex forward modeling. Our algorithm is not accurate to the level of traditional iodine technique. However it is convenient to use on a low-cost general-purpose spectrograph targeting a moderate Radial Velocity (RV) precision at a few 10-100~$\textrm{ms}^{-1}$ level. Finally, we have demonstrated the usefulness of our approach by measuring the RV signal of a well known short-period, planet-hosting star.

Measurements of atmospheric turbulence parameters at Vainu Bappu Observatory using short-exposure CCD images

We report atmospheric turbulence parameters, namely atmospheric seeing, tilt-anisoplanatic angle (θ0) and coherence time (τ0), measured under various sky conditions, at Vainu Bappu Observatory in Kavalur. Bursts of short exposure images of selected stars were recorded with a high-speed, frame-transfer CCD mounted on the Cassegrain focus of a newly commissioned 1.3 m telescope. The estimated median seeing is ≈ 1.85″ at wavelength of ∼ 600 nm, the image motion correlation between different pairs of stars is ∼ 44% for θ0 ≈ 36″ and mean τ0 is ≈ 2.4 ms. This work was motivated by the design considerations and expected performance of an adaptive optics system that is currently being planned for the telescope.

Stability analysis of VBT Echelle spectrograph for precise radial velocity measurements

A fiber-fed Echelle spectrograph at 2.3 m Vainu Bappu Telescope (VBT), Kavalur, has been in operation since 2005. Owing to various technological advancements in precision spectroscopy in recent years, several research avenues have been opened in observational astronomy. These developments have created a demand to improve the Doppler precision of our spectrograph. Currently, the stability of the instrument is compromised by the temperature and pressure fluctuations inside the Echelle room. Further, a better wavelength calibration approach is needed to carefully track and disentangle the instrumental effects from stellar spectra. While planning a possible upgrade with an Iodine absorption gas cell, we measured the raw stability of the spectrograph using a series of calibration frames taken with the ThAr gas discharge lamp. The time series data were analysed with cross-correlation method and the shift in ThAr emission lines was accurately measured across different Echelle orders. In this paper, we present our stability analysis methodology and results for the Kavalur spectrograph. We also identify possible sources of error and discuss our strategy to mitigate them.

Analysis of mutual events of Galilean satellites observed from VBO during 2014–2015

Results of analysis of 23 events of the 2014-2015 mutual event series from the Vainu Bappu Observatory are presented. Our intensity distribution model for the eclipsed/occulted satellite is based on the criterion that it simulates a rotational light curve that matches the ground based light curve. Dichotomy in the scattering characteristics of the leading and trailing sides explain the basic shape of the rotational light curves of Europa, Ganymede and Callisto. In case of Io the albedo map from USGS along with global values of scattering parameters work well. Mean values of residuals in $(O-C)$ along and perpendicular to the track are found to be -3.3 and -3.4 mas respectively compared to "L2" theory for the seven 2E1/2O1 events. The corresponding R.M.S values are 8.7 and 7.8 mas respectively. For the five 1E3/1O3 events, the along and perpendicular to the track mean residuals are 5.6 and 3.2 mas respectively. The corresponding R.M.S. residuals are 6.8 and 10.5 mas respectively. We compare the results using the chosen model (Model 1) with a uniform but limb darkened disk (Model 2). The residuals with Model 2 of the 2E1/2O1 and 1E3/1O3 events indicate a bias along the satellite track. The extent and direction of bias is consistent with the shift of the light center from the geometric center. Results using Model 1, which intrinsically takes into account the intensity distribution show no such bias.

SS 433: results of a recent multiwavelength campaign

We conducted a multiwavelength campaign in 2002 September-October, to observe SS 433. We used the Giant Meter Radio Telescope for radio observations, the Physical Research Laboratory Infrared Telescope at Mt Abu for infrared (IR), the ARIES telescope at Nainital for optical photometry, the telescope at the Vainu Bappu observatory for spectral measurements and the Rossi X-ray Timing Explorer for X-ray observations. We find sharp variations in intensity on time-scales of a few minutes in the X-ray, IR and radio wavelengths. Differential photometry in the IR observations clearly indicates significant intrinsic variations on short time-scales of minutes throughout the campaign. Combining the results for these wavelengths, we find a signature of delay of about two days between the IR and radio signals. The X-ray spectrum yielded double Fe line profiles which corresponded to red and blue components of the relativistic jet. We also present the broad-band spectrum averaged over the campaign duration.

High resolution stellar spectroscopy with VBT echelle spectrometer

The optical design and performance of the recently commissioned fiber fed echelle spectrometer of 2.34 meter Vainu Bappu Telescope are described. The use of it for stellar spectroscopic studies is discussed.

Investigations of the Rotation Pole from the Morphology of Dust Fans of Comet 81P/Wild 2

Investigations of the dust morphology of comet 81P/Wild 2 in the I- and R-band images obtained on 1997 May 15 from the Vainu Bappu Observatory, Kavalur, India, are presented. We model the trajectories of dust grains ejected from distributed sources on this comet to explain the morphology of the fans in these images and in the published images by Schulz and coworkers. We derive the pole position of αp = 297° ± 5° and δp = -10° ± 5°. Broad sources at +80° ± 5° and -25° ± 5° latitudes best explain the northern and southern fans, respectively.

An Optical, Dual-Beam, Automated Medium Resolution Spectropolarimeter for the Vainu Bappu Telescope

Fabrication of an optical dual-beam spectropolarimeter as an add-on facility to an existing astronomical spectrograph at the Vainu Bappu Telescope is described. The polarimetric optics consists of a superachromatic Pancharatnam design half-wave plate and a modified Glan-Taylor polarizing beam splitter. Instrumental response, calibration and characterization of the system are presented. Performance of the spectropolarimeter has been assessed based on the results of observations of polarized and unpolarized standard stars. The attainable accuracy of the instrument is found to be dependent on the S/N of the data. The present data set yields an accuracy of ∼ ±0.5% at 4000 A and ∼ ±0.3% at 7500 A, at a spectral resolution of ∼7.2 A. Analysis of spectropolarimetric data is systematically covered for removal of instrumental errors. The spectropolarimetric reduction software (SPRS), extremely versatile, user friendly and compatible with the IRAF image processing package, was developed for reducing spectropolarimetric data. The empirical relation by Serkowski (IAU Symposium 52, Interstellar Dust and Related Topics, J. M. Greenberg and H. C. van de Hulst (eds.), Dordrecht, Reidel, 1975, p. 145) for wavelength dependence of polarization due to interstellar medium has been fitted to the data for the star HD 43384 (9 Gem). Our result shows a polarization larger by 0.49% from Hsu and Berger (ApJ 262, 1982, 732). We attribute this difference to the long term variation in P for this star.

Fractal structure of the Horsehead nebula (B 33)

Analysis of the CCD image of the Horsehead nebula (B 33), taken in the H α (6561 A) using the 2.34 m Vainu Bappu Telescope (VBT) at Kavalur, India, is performed to test its fractal structure. Ten sample readings of the box dimension of this image were taken using a fractal analysis software, giving an average value of 1.6965725. The sample dimensions were found to be different from the topological dimension of one. Importantly, the box dimension of B 33 was not found to be significantly different from that of the Julia set (box dimension 1.679594) with c = −0.745429 + 0.113008i. This provides compelling evidence to show that the structure of the Horsehead nebula is not only fractal, but also that its geometry can be described by the Julia function f (z) = z 2 + c, where both z and c are complex numbers.

Astrometry from CCD photometry of mutual events of Jovian satellites from VBO during 1997

Astrometric results of CCD observations of the mutual events of the Galilean satellites of Jupiter from the Vainu Bappu Observatory are presented. The shifts in the photo-centers on the disks of Io and Europa due to albedo variations inferred from the available mosaics of Galileo imagery are determined. The estimated shifts from ≈ 90 km East to ≈ 50 km West on Io and from ≈ 50 km East to ≈ 30 km West for Europa during one orbital period are comparable to the accuracies provided by the present-day ephemerides. In a given mutual event series, the mutual events involving a given satellite pair dominate in number and occur nearly at the same orbital longitude within ± ; all the events are therefore delayed or all of them advanced depending on the direction of the shift of the photo-center. The implications of including these cumulative and sustained longitude residuals on the constructed ephemerides are discussed.