Exoplanet Group at PRL

We at PRL started a dedicated exoplanet program in 2008 for the first time in India with the development of a high-resolution spectrograph PARAS, which works at a resolution of 65,000. The primary aim was to detect the exoplanets around F, G and K dwarfs using the precision Radial Velocity (RV) technique. The spectrograph was commissioned and attached to the PRL 1.2m telescope at Gurushikhar Observatory,

The target was identified as a potential exoplanet host with the photometry data from the K2 telescope. The photometric data combined with false positive probability calculations wasn’t sufficient to confirm the planetary scenario. Therefore, a high-resolution spectroscopic follow-up of the target using the PARAS spectrograph (19 RV observations) was done over a period of 420 days. The planet has a radius of 6.12 ± 0.1 R⊕, and a mass of 27 (+14,-12.6) M⊕. This results in the Saturn-like density of ρp = 0.65 (+0.34, -0.30) g cm-3. This exoplanet is very important as it adds to a sparse catalogue of confirmed exoplanets with masses between 10 and 70 M⊕ and radii between 4 and 8 R⊕, whose masses and radii are measured to a precision of 50% or better (only 23 including that work) at that time.

We have also been part of the discovery of an intermediate-mass transiting brown dwarf (BD), TOI-503b, which is the first BD discovered from TESS as well as PARAS. The mass of TOI-503b was estimated to be ~54 Jupiter Mass (MJ) and 9 high-resolution spectra acquired from the PARAS spectrograph in 2019, majorly contributing to the mass-measurement of the BD. TOI-503b revolves around a metallic-line A-type star in 3.67718±0.0001 days of orbit. This discovery was joint work of a team from PRL, India, and CFA, Harvard, USA and KESPRINT Consortium, Europe.

Mount Abu, Rajasthan, India in late 2012. But the spectrograph became fully operational in late 2013 - early 2014. The spectrograph has shown RV stability of 1-2 m/s on bright RV standard stars like tau-Ceti, sigma-Draconis etc. In the initial phase of operation, a few very low-mass stars close to the star brown dwarf mass boundary were detected in F+M binary systems. One of them was BD+29 4980B, which is a ~100 Jupiter mass very late M dwarf around an early K-type main sequence star.

The breakthrough came in 2018 when we discovered a sub-Saturn kind of exoplanet around a Sun-type star K2-236 (Vmag = 10.15, G0 spectral-type) in a ~20 days orbit. This is the first-ever discovery of an exoplanet from India using PARAS, PRL as well as Indian scientists.

In the year 2021, we discovered a hot Jupiter at an orbital period of 3.208664 ± 0.000015 days around TOI-1789, identified as an exoplanetary candidate with TESS data. A ground-based photometry follow-up was also done using the PRL 43cm telescope with the Bessel-R filter confirming the transiting event on the host star. The high-precision RV observations were obtained from the high-resolution spectrographs, PARAS at PRL, India, and TCES at Thüringer Landessternwarte Tautenburg (TLS), Germany.

We find that TOI-1789 b has a mass of MP = 0.70 ± 0.16 Mj , a radius of RP =1.44 (+0.24,-0.14) Rj , and a bulk density of ρp = 0.28 (+0.14, -0.12) g cm-3 with an orbital separation of a = 0.04882 (+0.00063, -0.0016)AU. This is the second exoplanet discovered with PARAS. This is an inflated hot Jupiter, which is among the 8 rare exoplanets that are orbiting evolved stars in very close proximity.

Recently, we discovered the most extremely dense giant planet known to this date (density ~14 g cm−3) and mass of 12.69 (0.59, -0.6) Mj with TESS and PARAS. This astrophysical body lies at the boundary of planets and brown dwarfs and thus its discovery is extremely important. The research work appeared in Astronomy & Astrophysics Letters. The planet has a radius of 1.043 (0.04, -0.036) Rj, and an orbital period of 7.24600±0.00022 days. The eccentricity of ~0.306 and an orbital separation of ~0.0888 AU from its host star, suggests that the planet is likely undergoing high eccentricity tidal (HET) migration.

Since mid-2018, we have also started working on the design and development of a next-generation spectrograph to the existing PARAS, named PARAS-2, which was recently commissioned and attached to the PRL’s new 2.5m telescope at the same observatory. PARAS-2 aimed to achieve sub-m s−1 RV precision, which is necessary to detect and characterize super-Earths or massive planets around G and K dwarf stars. The larger aperture of the 2.5m telescope allows for the observation of fainter objects, expanding the capabilities of exoplanetary research. In the engineering tests of PARAS-2, we have consistently observed the dispersion in the inter-fiber drift to be 20-40 cm s−1 which clearly demonstrates that PARAS-2 is capable of reaching precision in the order of sub-m s−1. The double scrambler for PARAS-2 has been designed and currently under fabrication process. It is expected to be installed by March 2024. We expect on-sky RV precision on bright RV standard stars to be close to the intrinsic limit of the instrument (30-50 cm s−1).

Current Team Members: -

Prof. Abhijit Chakraborty (P.I.), Mr. Kapil Kumar, Mr. Neelam JSSV Prasad, Mr. Rishikesh Sharma, Mr. Kevikumar Lad, Mr. Ashirbad Nayak, Ms. Nikitha Jithendran, Mr. Churchil Dwivedi

Past Team Members who left or superannuated: -

Mr. Vaibhav Dixit, Mr. Vishal Shah, Mr. Dishendra

Current Postdocs: -

Dr. Akanksha Khandelwal

Dr. Alexander Panchal

Current PhD Students: -

Mr. Sanjay Baliwal, Mr. Shubhendra Das

Past PhD students: -

Dr. Priyanka Chaturvedi

Persons who have given very important technical advises to the PARAS team:-

Prof. Frencesco Pepe, Geneva Observatory, Switzerland

Prof. Andrew Szentgyorgyi, CFA, Harvard, USA

Past Collaborators: -

Prof. Suvrath Mahadevan, and Dr. Arpita Roy, Penn State University, Pennsalviniya, USA

Important Preprint on PARAS-2 and PRL 2.5m telescope: The PRL 2.5m Telescope and its First Light Instruments: FOC & PARAS-2 Abhijit CHAKRABORTY, Kapil Kumar BHARADWAJ, J.S.S.V.Prasad NEELAM , Rishikesh SHARMA, Kevikumar A. LAD, Ashirbad NAYAK, Nikitha JITHENDRAN, Vishal JOSHI, Vivek Kumar MISHRA and Nafees AHMED. To be published in to be published in the Bulletin of Liège Royal Society of Sciences. The preprint can be downloaded from the PRL Observatory webpage.

Important Publications: -

  • Khandelwal, Akanksha, Sharma, Rishikesh; Chakraborty, Abhijit; , et al., 2023, “Discovery of a massive giant planet with extreme density around the sub-giant star TOI-4603”, A & A Letters, 672, L7, doi: 10.1051/0004-6361/202245608

  • Khandelwal, Akanksha, Chaturvedi, Priyanka; Chakraborty, Abhijit; Sharma, Rishikesh, et al., 2021, “Discovery of an inflated hot Jupiter around a slightly evolved star TOI-1789”, MNRAS, 509, 3, 3339-3354, doi: 10.1093/mnras/stab2970

  • Subjak, Jan, Sharma, Rishikesh, Carmichael, Theron W., et al. 2019, “TOI-503: The First Known Brown-dwarf Am-star Binary from the TESS Mission”, 2020, AJ, 159, 4, 151, doi: 10.3847/1538-3881/ab7245

  • Chakraborty, Abhijit; Roy, Arpita; Sharma, Rishikesh; Mahadevan, Suvrath; Chaturvedi, Priyanka; Prasad, Neelam J. S. S. V.; Anandarao, B. G. “Evidence of a Sub-Saturn around EPIC 211945201”, 2018AJ....156....3

  • Abhijit Chakraborty; Nitesh Thapa; Kapil Kumar; Prasad J. S. S. V. Neelam; Rishikesh Sharma; Arpita Roy; “PARAS-2 Precision radial velocimeter: optical and mechanical design of a fiber-fed high-resolution spectrograph under vacuum and temperature control”, Proc. SPIE 10702, Ground based and Airborne Instrumentation for Astronomy VII, 107026G (20 July 2018); doi: 10.1117/12.2313055

  • Chakraborty, Abhijit; Mahadevan, Suvrath; Roy, Arpita; Dixit, Vaibhav; Richardson, Eric; Dongre, Varun; Pathan, F.; Chaturvedi, Priyanka; Shah, Vishal; Ubale, Girish; Anandarao, B.G. (2013). The PRL Stabilized High Resolution Echelle Fiber-fed Spectrograph: Instrument Description & First Radial Velocity Results. Publications of the Astronomical Society of the Pacific. 126. 10.1086/675352.

Other Publications: -

  • Sharma, Rishikesh & Chakraborty, Abhijit, “Precision wavelength calibration for radial velocity measurements using uranium lines between 3800 and 6900 Å”, 2021, JATIS-SPIE, 7, 38005, doi: 10.1117/1.JATIS.7.3.038005

  • Chaturvedi, Priyanka; Sharma, Rishikesh; Chakraborty, Abhijit; Anandarao, B. G.; Prasad, Neelam J. S. S. V., “Masses and Radii of Four Very Low-mass Stars in F+M Eclipsing Binary Systems” 2018AJ....156...27C

  • Chaturvedi, Priyanka, Abhijit Chakraborty, and B. G. Anandarao. "Spectral Analysis Code: PARAS SPEC." arXiv e-prints (2016): arXiv:1610.07235. doi: 10.48550/arXiv.1610.07235.

  • Chaturvedi, Priyanka, Rohit Deshpande, Vaibhav Dixit, Arpita Roy, Abhijit Chakraborty, Suvrath Mahadevan, B. G. Anandarao, Leslie Hebb, and P. Janardhan. "Determination of mass and orbital parameters of a low-mass star HD 213597B." Monthly Notices of the Royal Astronomical Society 442, no. 4 (2014): 3737-3744. doi: 10.1093/mnras/stu1127.

  • Chaturvedi, Priyanka, Abhijit Chakraborty, B. G. Anandarao, Arpita Roy, and Suvrath Mahadevan. "Detection of a very low mass star in an eclipsing binary system." Monthly Notices of the Royal Astronomical Society 462, no. 1 (2016): 554-564. doi: 10.1093/mnras/stw1560.

  • Roy, Arpita, Abhijit Chakraborty, Suvrath Mahadevan, Priyanka Chaturvedi, Neelam J. S. S. V. Prasad, Vishal Shah, F. M. Pathan, and B. G. Anandarao. "Precision velocimetry planet hunting with PARAS: current performance and lessons to inform future extreme precision radial velocity instruments." In Ground-based and Airborne Instrumentation for Astronomy VI, edited by Christopher J. Evans, Luc Simard, and Hideki Takami. Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Volume 9908, August 2016, Article ID 99086R. doi: 10.1117/12.2232833.

  • Fischer, Debra A., Guillem Anglada-Escude, Pamela Arriagada, Roman V. Baluev, Jacob L. Bean, Francois Bouchy, Lars A. Buchhave, Thorsten Carroll, Abhijit Chakraborty, Justin R. Crepp, Rebekah I. Dawson, Scott A. Diddams, Xavier Dumusque, Jason D. Eastman, Michael Endl, Pedro Figueira, Eric B. Ford, Daniel Foreman-Mackey, Paul Fournier, Gabor Fürész, B. Scott Gaudi, Philip C. Gregory, Frank Grundahl, Artie P. Hatzes, Guillaume Hébrard, Enrique Herrero, David W. Hogg, Andrew W. Howard, John A. Johnson, Paul Jorden, Colby A. Jurgenson, David W. Latham, Greg Laughlin, Thomas J. Loredo, Christophe Lovis, Suvrath Mahadevan, Tyler M. McCracken, Francesco Pepe, Mario Perez, David F. Phillips, Peter P. Plavchan, Lisa Prato, Andreas Quirrenbach, Ansgar Reiners, Paul Robertson, Nuno C. Santos, Damien Segransan, Alessandro Sozzetti, Tilo Steinmetz, Andrew Szentgyorgyi, Stéphane Udry, Jeff A. Valenti, Sharon X. Wang, Robert A. Wittenmyer, and Jason T. Wright. "State of the Field: Extreme Precision Radial Velocities." Publications of the Astronomical Society of the Pacific 128, no. 964 (2016): 066001. doi: 10.1088/1538-3873/128/964/066001.

  • Kane, Stephen R., Robert A. Wittenmyer, Natalie R. Hinkel, Arpita Roy, Suvrath Mahadevan, Diana Dragomir, Jaymie M. Matthews, Gregory W. Henry, Abhijit Chakraborty, Tabetha S. Boyajian, Jason T. Wright, David R. Ciardi, Debra A. Fischer, R. Paul Butler, C. G. Tinney, Brad D. Carter, Hugh R. A. Jones, Jeremy Bailey, and Simon J. O'Toole. "Evidence for Reflected Light from the Most Eccentric Exoplanet Known." The Astrophysical Journal 821, no. 1 (2016): 65. doi: 10.3847/0004-637X/821/1/65.