Browsing by Author "Banerjee, Bihan"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    A uGMRT search for radio emission from planets around evolved stars
    (2024) Narang, Mayank; Puravankara, M.; Chandra, C. H. Ishwara; Banerjee, Bihan; Tyagi, Himanshu; Tamura, Motohide; Henning, Thomas; Mathew, Blesson; Lazio, Joseph; Surya, Arun; Nayak, Prasanta K.
    In this work, we present the results from a study using the Giant Meterwave Radio Telescope (GMRT) to search for radio emission from planets around three evolved stars namely alpha Tau, beta UMi, and beta Gem. Both alpha Tau and beta UMi host massive similar to 6 MJ mass planets at about similar to 1.4 au from the central star, while beta Gem is host to a 2.9 MJ mass planet at 1.7 au from the host star. We observe alpha Tau and beta UMi at two upgraded GMRT bands: band 3 (250-500 MHz) and band 4 (550-900 MHz). We also analysed the archival observations from beta Gem at 150 MHz from GMRT. We did not detect any radio signals from these systems. At 400 MHz, the 3 sigma upper limit is 87 mu Jy beam(-1) for alpha Tau b and 77.4 mu Jy beam(-1) for beta UMi b. From our observations at 650 MHz, we place a 3 sigma upper limit of 28.2 mu Jy beam(-1) for alpha Tau b and 33.6 mu Jy beam(-1) for beta UMi b. For beta Gem b, at 150 MHz, we place an upper limit of 2.5 mJy. At 400 and 650 MHz, our observations are the deepest radio images for any exoplanetary system.
  • Thumbnail Image
    Item
    Host-star Properties of Hot, Warm, and Cold Jupiters in the Solar Neighborhood from Gaia Data Release 3: Clues to Formation Pathways
    (2024) Banerjee, Bihan; Narang, Mayank; Manoj, P.; Henning, Thomas; Tyagi, Himanshu; Surya, Arun; Nayak, Prasanta K.; Tripathi, Mihir
    Giant planets exhibit diverse orbital properties, hinting at their distinct formation and dynamic histories. In this paper, using Gaia Data Release 3 (DR3), we investigate if and how the orbital properties of Jupiters are linked to their host star properties, particularly their metallicity and age. We obtain metallicities for main-sequence stars of spectral type F, G, and K, hosting hot, warm, and cold Jupiters with varying eccentricities. We compute the velocity dispersions of the host stars of these three groups using kinematic information from Gaia DR3 and obtain average ages using a velocity dispersion-age relation. We find that the host stars of hot Jupiters are relatively metal rich ([Fe/H] = 0.18 +/- 0.13) and young (median age of 3.97 +/- 0.51 Gyr) compared to the host stars of cold Jupiters in nearly circular orbits, which are relatively metal poor (0.03 +/- 0.18) and older (median age of 6.07 +/- 0.79 Gyr). The host stars of cold Jupiters in high-eccentricity orbits, on the other hand, show metallicities similar to those of the hosts of hot Jupiters, but are older, on average (median age of 6.25 +/- 0.92 Gyr). The similarity in metallicity between the hosts of hot Jupiters and the hosts of cold Jupiters in high-eccentricity orbits supports high-eccentricity migration as the potential origin of hot Jupiters, with the latter serving as the progenitors of hot Jupiters. However, the average age difference between them suggests that the older hot Jupiters may have been engulfed by their host star over timescales similar to 6 Gyr. This allows us to estimate the value of stellar tidal quality factor, Q * ' similar to 10 6 +/- 1 .
  • No Thumbnail Available
    Item
    Identifying the population of T-Tauri stars in Taurus: UV-optical synergy
    (2023) Nayak, Prasanta K.; Narang, Mayank; Puravankara, Manoj; Tyagi, Himanshu; Banerjee, Bihan; Sharma, Saurabh; Pandey, Rakesh; Surya, Arun; Mathew, Blesson; Arun, R.; Ujjwal, K.; Kartha, Sreeja S.
    With the third data release of the Gaia mission, Gaia DR3 with its precise photometry and astrometry, it is now possible to study the behavior of stars at a scale never seen before. In this paper, we developed new criteria to identify T-Tauri stars (TTS) candidates using UV and optical color-magnitude diagrams (CMDs) by combining the GALEX and Gaia surveys. We found 19 TTS candidates and five of them are newly identified TTS in the Taurus molecular cloud (TMC), not cataloged before as TMC members. For some of the TTS candidates, we also obtained optical spectra from several Indian telescopes. We also present the analysis of distance and proper motion of young stars in the Taurus using data from Gaia DR3. We found that the stars in Taurus show a bimodal distribution with distance, having peaks at 130.17(-1.24)(1.31) pc and 156.25(-5.00)(1.86) pc. The reason for this bimodality, we think, is due to the fact that different clouds in the TMC region are at different distances. We further showed that the two populations have similar ages and proper motion distribution. Using the Gaia DR3 CMD, we showed that the age of Taurus is consistent with 1 Myr.
  • No Thumbnail Available
    Item
    Optical spectroscopy of Gaia detected protostars with DOT: Can we probe protostellar photospheres?
    (2023) Narang, Mayank; Manoj, P.; Tyagi, Himanshu; Nayak, Prasanta K.; Sharma, Saurabh; Surya, Arun; Banerjee, Bihan; Mathew, Blesson; Ghosh, Arpan; Verma, Aayushi
    Optical spectroscopy offers the most direct viewof the stellar properties and the accretion indicators. Standard accretion tracers, such as H beta, H alpha and Ca II triplet lines, and most photospheric features fall in the opticalwavelengths. However, these tracers are not readily observable from deeply embedded protostars because of the large line of sight extinction (A(v) similar to 50-100 mag) toward them. In some cases, however, it is possible to observe protostars at optical wavelengths if the outflow cavity is aligned along the line-of-sight that allows observations of the photosphere, or the envelope is very tenuous and thin, such that the extinction is low. In such cases, we not only detect these protostars at optical wavelengths, but also follow up spectroscopically. We have used the HOPS catalog (Furlan et al. in 2016) of protostars in Orion to search for optical counterparts for protostars in the Gaia DR3 survey. Out of the 330 protostars in the HOPS sample, an optical counterpart within 2 '' is detected for 62 of the protostars. For 17 out of 62 optically detected protostars, we obtained optical spectra (between 5500 and 8900 angstrom) using nt Object Spectrograph and Camera (ADFOSC) on the 3.6-m Devasthal Optical Telescope (DOT) and Hanle Faint Object Spectrograph Camera (HFOSC) on 2-m Himalayan Chandra Telescope (HCT). We detect strong photospheric features, such as the TiO bands in the spectra (of 4 protostars), hinting that photospheres can form early in the star-formation process. We further determined the spectral types of protostars, which show photospheres similar to a late M-type. Mass accretion rates derived for the protostars are similar to those found for T-Tauri stars, in the range of 10(-7)-10(-8) M-circle dot yr(-1).
  • No Thumbnail Available
    Item
    uGMRT Survey of EXoplanets Around M-dwarfs (GS-EXAM): Radio Observations of GJ 1151
    (2024) Narang, Mayank; Puravankara, Manoj; Vedantham, H. K.; Ishwara-Chandra, C. H.; De, Ayanabha; Tyagi, Himanshu; Banerjee, Bihan; Nayak, Prasanta K.; Surya, Arun; Shridharan, B.; Pathak, Vinod C.; Tripathi, Mihir
    Coherent radio emission with properties similar to planetary auroral signals has been reported from GJ 1151, a quiescent, slow-rotating mid-M star, by the LOFAR Two-meter (120-170 MHz) Sky Survey. The observed LOFAR emission is fairly bright at 0.89 mJy with 64% circular polarization, and the emission characteristics are consistent with the interaction between an Earth-sized planet with an orbital period of 1-5 days and the magnetic field of the host star. However, no short-period planet has been detected around GJ 1151. To confirm the reported radio emission caused by the putative planet around GJ 1151 and to investigate the nature of this emission, we carried out upgraded Giant Metrewave Radio Telescope observations of GJ 1151 at 150, 218, and 400 MHz over 33 hr across ten epochs. No emission was detected at any frequency. While at 150 and 218 MHz, nondetection could be due to the low sensitivity of our observations, at 400 MHz, the rms sensitivities achieved were sufficient to detect the emission observed with LOFAR at similar to 20 sigma level. Our findings suggest that the radio emission is highly time variable, likely influenced by the star-planet system's phase and the host star's magnetic field. Additional observations below 170 MHz, at more frequent epochs (as the periodicity of the emission is unknown), especially during periods of high stellar magnetic field strength, are needed to confirm the emission.