The past decade has seen increasing efforts in detecting and characterising exoplanets using high-contrast imaging in the near- and mid-infrared, which is the optimal wavelength domain for studying ...old, cold planets. In this work, we present deep adaptive optics imaging observations of the nearby Sun-like star ɛ Ind A with the NaCo (L') and NEAR (10-12.5 microns) instruments at VLT in an attempt to directly detect its planetary companion, whose presence has been indicated from radial velocity (RV) and astrometric trends. We derive brightness limits from the non-detection of the companion with both instruments and interpret the corresponding sensitivity in mass based on both cloudy and cloud-free atmospheric and evolutionary models. For an assumed age of 5 Gyr for the system, we get detectable mass limits as low as 4.4 MSUBJ/SUB in NaCo L' and 8.2 MSUBJ/SUB in NEAR bands at 1.5'' from the central star. If the age assumed is 1 Gyr, we reach even lower mass limits of 1.7 MSUBJ/SUB in NaCo L' and 3.5 MSUBJ/SUB in NEAR bands at the same separation. However, based on the dynamical mass estimate (3.25 MSUBJ/SUB) and ephemerides from astrometry and RV, we find that the non-detection of the planet in these observations puts a constraint of 2 Gyr on the lower age limit of the system. NaCo offers the highest sensitivity to the planetary companion in these observations, but the combination with the NEAR wavelength range adds a considerable degree of robustness against uncertainties in the atmospheric models. This underlines the benefits of including a broad set of wavelengths for the detection and characterisation of exoplanets in direct imaging studies. Based on archival observations from the European Southern Observatory, Chile (Programmes 0102.C-0592 and 60.A-9107).
We have followed up on our observations of the ~ 40-Myr, and still accreting, PMC Delorme 1 (AB)b. We used high-resolution spectroscopy to characterise the accretion process further by accessing the ...wealth of emission lines in the near-UV. With VLT/UVES, we obtained R ~ 50000 spectroscopy at 330--452 nm. After separating the emission of the companion from that of the M5 low-mass binary, we performed a detailed emission-line analysis, which included planetary accretion shock modelling. We reaffirm ongoing accretion in Delorme 1 (AB)b and report the first detections in a (super-Jovian) protoplanet of resolved hydrogen line emission in the near-UV (H-gamma, H-delta, H-epsilon, H8 and H9). We tentatively detect H11, H12, He I and Ca II H/K. The analysis strongly favours a planetary accretion shock with a line-luminosity-based accretion rate dMp/dt = 2e-8 MJ/yr. The lines are asymmetric and well described by sums of narrow and broad components with different velocity shifts. Overall line shapes are best explained by a pre-shock velocity v0 = 170+-30 km/s, implying a planetary mass Mp = 13+-5 MJ, and number densities n0 ~ 1e13/cc or n0 ~ 1e11/cc. The higher density implies a small line-emitting area of ~ 1% relative to the planetary surface. This favours magnetospheric accretion, a case potentially strengthened by the presence of blueshifted emission in the asymmetrical profiles.High-resolution spectroscopy offers the opportunity to resolve line profiles, crucial for studying the accretion process in depth. The super-Jovian protoplanet Delorme 1 (AB)b is still accreting at ~ 40 Myr. Thus, Delorme 1 belongs to the growing family of Peter Pan disc systems with protoplanetary and/or circumplanetary disc(s) far beyond the typically assumed disc lifetimes. Further observations of this benchmark companion, and its presumed disc(s), will help answer key questions about the accretion geometry in PMCs.
Recent observations from B-star Exoplanet Abundance Study (BEAST) have illustrated the existence of sub-stellar companions around very massive stars. In this paper, we present the detection of two ...lower mass companions to a relatively nearby (\(148.7^{+1.5}_{-1.3}\) pc), young (\(17^{+3}_{-4}\) Myr), bright (V=\(6.632\pm0.006\) mag), \(2.58\pm0.06~ M_{\odot}\) B9V star HIP 81208 residing in the Sco-Cen association, using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope (VLT) in Chile. Analysis of the photometry obtained gives mass estimates of \(67^{+6}_{-7}~M_J\) for the inner companion and \(0.135^{+0.010}_{-0.013}~M_{\odot}\) for the outer companion, indicating the former to be most likely a brown dwarf and the latter to be a low-mass star. The system is compact but unusual, as the orbital planes of the two companions are likely close to orthogonal. The preliminary orbital solutions we derived for the system indicate that the star and the two companions are likely in a Kozai resonance, rendering the system dynamically very interesting for future studies.
Most (~82%) of the over 4000 confirmed exoplanets known today orbit very close to their host stars, within 0.5 au. Planets at such small orbital distances can result in significant interactions with ...their host stars, which can induce increased activity levels in them. In this work, we have searched for statistical evidence for Star-Planet Interactions (SPI) in the ultraviolet (UV) using the largest sample of 1355 GALEX detected host stars with confirmed exoplanets and making use of the improved host star parameters from Gaia DR2. From our analysis, we do not find any significant correlation between the UV activity of the host stars and their planetary properties. We further compared the UV properties of planet host stars to that of chromospherically active stars from the RAVE survey. Our results indicate that the enhancement in chromospheric activity of host stars due to star-planet interactions may not be significant enough to reflect in their near and far UV broad band flux.
This licentiate thesis provides a broad introduction into the methodology of detecting and characterising exoplanets, with the main focus on the method of high-contrast imaging (HCI). Developments in ...theoretical knowledge as well as instrumentation have, in the past decade, pushed the boundaries of what HCI can achieve, both in terms of detection sensitivity and constraining planet properties. Direct imaging surveys in the near infrared (NIR) and longward wavelengths have proven particularly useful in detecting younger giant planets at wide orbital separations. The scientific work presented as part of this thesis is one such result of an imaging pursuit of the young giant planet, ϵ Ind Ab, which has long eluded NIR imaging surveys in the past, yet revealing its existence via radial velocity trends and astrometry of the parent star. It resides in the very interesting ϵ Ind stellar system, revolving around the primary star ϵ Ind A which is a Sun-like star only ∼12 light years away and visible in the night sky to the naked eye. With the combination of imaging data from two mid infrared (MIR) instruments, advanced post-processing techniques as well as comparative analysis using different planet atmospheric models, this work was able to place tight constraints on the age of the system and mass of the planet, although no detection was achieved. The new constraints set a firm foundation for MIR imaging surveys for the planet in future, especially with the upcoming more sensitive, advanced instruments in the later half of the decade. MIR imaging surveys have gained increasing significance in the recent years, due to their ability to detect colder/ smaller planets. It plays an important role in covering the missing gaps in the planet parameter space, ultimately aiding in improving our knowledge on planet formation and evolution.
Narrow line Seyfert 1 galaxies (NLS1s) are believed to be powered by accretion of matter onto low mass black holes (BHs) in spiral host galaxies with BH masses M_BH of 10^6 - 10^8 M_sun . However, ...the broad band spectral energy distribution of the gamma-ray emitting NLS1s are found to be similar to flat spectrum radio quasars. This challenges our current notion of NLS1s having low M_BH . To resolve this tension of low M_BH values in NLS1s, we fitted the observed optical spectrum of a sample of radio-loud NLS1s (RL-NLS1s), radio-quiet NLS1s (RQ-NLS1s) and radio-quiet broad line Seyfert 1 galaxies (RQ-BLS1s) of about 500 each with the standard Shakura-Sunyaev accretion disk (AD) model. For RL-NLS1s we found a mean log(M_ADBH/M_sun) of 7.98 +/- 0.54. For RQ-NLS1s and RQ-BLS1s we found mean log(M_ADBH/M_sun) of 8.00 +/- 0.43 and 7.90 +/- 0.57, respectively. While the derived M_BH values of RQ-BLS1s are similar to their virial masses, for NLS1s the derived M_ADBH values are about an order of magnitude larger than their virial estimates. Our analysis thus indicates that NLS1s have M_BH similar to RQ-BLS1s and their available virial M_BH values are underestimated influenced by their observed relatively small emission line widths. Considering Eddington ratio as an estimation of the accretion rate and using M_ADBH, we found the mean accretion rate of our RQ-NLS1s, RL-NLS1s and RQ-BLS1s as 0.06 (+0.16, -0.05), 0.05 (+0.18, -0.04) and 0.05 (+0.15, -0.04) respectively. Our results therefore suggest that NLS1s have BH masses and accretion rates similar to BLS1s.
Planet formation occurs around a wide range of stellar masses and stellar system architectures. An improved understanding of the formation process can be achieved by studying it across the full ...parameter space, particularly toward the extremes. Earlier studies of planets in close-in orbits around high-mass stars have revealed an increase in giant planet frequency with increasing stellar mass until a turnover point at 1.9 solar masses, above which the frequency rapidly decreases. This could potentially imply that planet formation is impeded around more massive stars, and that giant planets around stars exceeding 3 solar masses may be rare or non-existent. However, the methods used to detect planets in small orbits are insensitive to planets in wide orbits. Here we demonstrate the existence of a planet at 560 times the Sun-Earth distance from the 6-10 solar mass binary b Centauri through direct imaging. The planet-to-star mass ratio of 0.10-0.17% is similar to the Jupiter-Sun ratio, but the separation of the detected planet is ~100 times wider than that of Jupiter. Our results show that planets can reside in much more massive stellar systems than what would be expected from extrapolation of previous results. The planet is unlikely to have formed in-situ through the conventional core accretion mechanism, but might have formed elsewhere and arrived to its present location through dynamical interactions, or might have formed via gravitational instability.
A&A 651, A89 (2021) The past decade has seen increasing efforts in detecting and characterising
exoplanets by high contrast imaging in the near/mid-infrared, which is the
optimal wavelength domain ...for studying old, cold planets. In this work, we
present deep AO imaging observations of the nearby Sun-like star $\epsilon$ Ind
A with NaCo ($L^{\prime}$) and NEAR (10-12.5 microns) instruments at VLT, in an
attempt to directly detect its planetary companion whose presence has been
indicated from radial velocity (RV) and astrometric trends. We derive
brightness limits from the non-detection of the companion with both
instruments, and interpret the corresponding sensitivity in mass based on both
cloudy and cloud-free atmospheric and evolutionary models. For an assumed age
of 5 Gyr for the system, we get detectable mass limits as low as 4.4 $M_{\rm
J}$ in NaCo $L^{\prime}$ and 8.2 $M_{\rm J}$ in NEAR bands at 1.5$\arcsec$ from
the central star. If the age assumed is 1 Gyr, we reach even lower mass limits
of 1.7 $M_{\rm J}$ in NaCo $L^{\prime}$ and 3.5 $M_{\rm J}$ in NEAR bands, at
the same separation. However, based on the dynamical mass estimate (3.25
$M_{\rm J}$) and ephemerides from astrometry and RV, we find that the
non-detection of the planet in these observations puts a constraint of 2 Gyr on
the lower age limit of the system. NaCo offers the highest sensitivity to the
planetary companion in these observations, but the combination with the NEAR
wavelength range adds a considerable degree of robustness against uncertainties
in the atmospheric models. This underlines the benefits of including a broad
set of wavelengths for detection and characterisation of exoplanets in direct
imaging studies.
The present study makes use of the unprecedented capability of the Gaia mission to obtain the stellar parameters such as distance, age, and mass of HAeBe stars. The accuracy of Gaia DR2 astrometry is ...demonstrated from the comparison of the Gaia DR2 distances of 131 HAeBe stars with the previously estimated values from the literature. This is one of the initial studies to estimate the age and mass of a confirmed sample of HAeBe stars using both the photometry and distance from the Gaia mission. Mass accretion rates are calculated from \(H\alpha\) line flux measurements of 106 HAeBe stars. Since we used distances and the stellar masses derived from the Gaia DR2 data in the calculation of mass accretion rate, our estimates are more accurate than previous studies. The mass accretion rate is found to decay exponentially with age, from which we estimated a disk dissipation timescale of \(1.9\pm 0.1\) Myr. Mass accretion rate and stellar mass exhibits a power law relation of the form, \(\dot{M}_{acc}\) \(\propto\) \(M_{*}^{2.8\pm0.2}\). From the distinct distribution in the values of the infrared spectral index, \(n_{2-4.6}\), we suggest the possibility of difference in the disk structure between Herbig Be and Herbig Ae stars.
The past decade has seen increasing efforts in detecting and characterising exoplanets by high contrast imaging in the near/mid-infrared, which is the optimal wavelength domain for studying old, cold ...planets. In this work, we present deep AO imaging observations of the nearby Sun-like star \(\epsilon\) Ind A with NaCo (\(L^{\prime}\)) and NEAR (10-12.5 microns) instruments at VLT, in an attempt to directly detect its planetary companion whose presence has been indicated from radial velocity (RV) and astrometric trends. We derive brightness limits from the non-detection of the companion with both instruments, and interpret the corresponding sensitivity in mass based on both cloudy and cloud-free atmospheric and evolutionary models. For an assumed age of 5 Gyr for the system, we get detectable mass limits as low as 4.4 \(M_{\rm J}\) in NaCo \(L^{\prime}\) and 8.2 \(M_{\rm J}\) in NEAR bands at 1.5\(\arcsec\) from the central star. If the age assumed is 1 Gyr, we reach even lower mass limits of 1.7 \(M_{\rm J}\) in NaCo \(L^{\prime}\) and 3.5 \(M_{\rm J}\) in NEAR bands, at the same separation. However, based on the dynamical mass estimate (3.25 \(M_{\rm J}\)) and ephemerides from astrometry and RV, we find that the non-detection of the planet in these observations puts a constraint of 2 Gyr on the lower age limit of the system. NaCo offers the highest sensitivity to the planetary companion in these observations, but the combination with the NEAR wavelength range adds a considerable degree of robustness against uncertainties in the atmospheric models. This underlines the benefits of including a broad set of wavelengths for detection and characterisation of exoplanets in direct imaging studies.
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