IRAS 22150+6109 – a young B-type star with a large disc Zakhozhay, Olga V; Miroshnichenko, Anatoly S; Kuratov, Kenesken S ...
Monthly notices of the Royal Astronomical Society,
06/2018, Letnik:
477, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We present the results of a spectroscopic analysis and spectral energy distribution (SED) modelling of the optical counterpart of the infrared source IRAS 22150+6109. The source was ...suggested to be a Herbig Be star located in the star-forming region L 1188. Absorption lines in the optical spectrum indicate a spectral type B3, while weak Balmer emission lines reflect the presence of a circumstellar gaseous disc. The star shows no excess radiation in the near-infrared spectral region and a strong excess in the far-infrared that we interpret as radiation from a large disc, the inner edge of which is located very far from the star (550 au) and does not attenuate its radiation. We conclude that IRAS 22150+6109 is an intermediate-mass star that is currently undergoing a short pre-main-sequence evolutionary stage.
Using numerical hydrodynamic simulations, we study the gravitational fragmentation of an unstable protostellar disc formed during the collapse of a pre-stellar core with a mass of 1.2 M. The forming ...fragments span a mass range from about a Jupiter mass to very low mass protostars and are located at distances from a few tens to a thousand au, with a dearth of objects at 100 au. We explore the possibility of observational detection of the fragments in discs viewed through the outflow cavity at a distance of 250 pc. We demonstrate that one hour of integration time with the Atacama Large Millimeter/sub-millimeter Array (ALMA) is sufficient to detect the fragments with masses as low as 1.5M
Jup at orbital distances up to 800 au from the protostar. The ALMA resolution sets the limit on the minimum orbital distance of detectable fragments. For the adopted resolution of our simulated ALMA images of 0.1 arcsec, the fragments can be detected at distances down to 50 au. At smaller distances, the fragments usually merge with the central density peak. The likelihood for detecting the fragments reduces significantly for a lower resolution of 0.5 arcsec. Some of the most massive fragments, regardless of their orbital distance, can produce characteristic peaks at 5 μm and hence their presence can be indirectly inferred from the observed spectral energy distributions of protostars.
HD 3167 is a bright (V = 8.9 mag) K0 V star observed by NASA's K2 space mission during its Campaign 8. It has recently been found to host two small transiting planets, namely, HD 3167b, an ...ultra-short-period (0.96 days) super-Earth, and HD 3167c, a mini-Neptune on a relatively long-period orbit (29.85 days). Here we present an intensive radial velocity (RV) follow-up of HD 3167 performed with the FIES@NOT, HARPS@ESO-3.6 m, and HARPS-N@TNG spectrographs. We revise the system parameters and determine radii, masses, and densities of the two transiting planets by combining the K2 photometry with our spectroscopic data. With a mass of 5.69 0.44 M⊕, a radius of 1.574 0.054 R⊕, and a mean density of , HD 3167b joins the small group of ultra-short-period planets known to have rocky terrestrial compositions. HD 3167c has a mass of M⊕ and a radius of R⊕, yielding a mean density of , indicative of a planet with a composition comprising a solid core surrounded by a thick atmospheric envelope. The rather large pressure scale height (∼350 km) and the brightness of the host star make HD 3167c an ideal target for atmospheric characterization via transmission spectroscopy across a broad range of wavelengths. We found evidence of additional signals in the RV measurements but the currently available data set does not allow us to draw any firm conclusions on the origin of the observed variation.
Context.
The existence of warm (protoplanetary) disks around very young isolated planetary and brown dwarf mass objects is known based on near- and mid-infrared flux excesses and millimeter ...observations. These disks may later evolve into debris disks or rings, although none have been observed or confirmed so far. Little is known about circum(sub)stellar and debris disks around substellar objects.
Aims.
We aim to investigate the presence of debris disks around two of the closest (~20 pc), young substellar companions, namely G196-3 B and VHS J125601.92–125723.9 b (VHS J1256–1257 b), whose masses straddle the borderline between planets and brown dwarfs. Both are companions at wide orbits (≥100 au) of M-type dwarfs and their ages (50–100 Myr and 150–300 Myr, respectively) are thought to be adequate for the detection of second-generation disks.
Methods.
We obtained deep images of G196-3 B and VHS J1256–1257 b with the NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm. These data were combined with recently published Atacama Large Millimeter Array (ALMA) and Very Large Array (VLA) data of VHS J1256–1257 b at 0.87 mm and 0.9 cm, respectively.
Results.
Neither G196-3 B nor VHS J1256–1257 b were detected in the NOEMA, ALMA, and VLA data. At 1.3 mm, we imposed flux upper limits of 0.108 mJy (G196-3 B) and 0.153 mJy (VHS J1256–1257 b) with a 3-
σ
confidence. Using the flux upper limits at the millimeter and radio wavelength regimes, we derived maximum values of 1.38×10
−2
M
Earth
and 5.46 × 10
−3
M
Earth
for the mass of any cold dust that might be surrounding G196-3 B and VHS J1256–1257 b, respectively.
Conclusions.
We put our results in the context of other deep millimeter observations of free-floating and companion objects with substellar masses smaller than 20
M
Jup
and ages between approximately one and a few hundred million years. Only two very young (2–5.4 Myr) objects are detected out of a few tens of them. This implies that the disks around these very low-mass objects must have small masses, and possibly reduced sizes, in agreement with findings by other groups. If debris disks around substellar objects scale down (in mass and size) in a similar manner as protoplanetary disks do, millimeter observations of moderately young brown dwarfs and planets must be at least two orders of magnitude deeper to be able to detect and characterize their surrounding debris disks.
The origin of the very red optical and infrared colours of intermediate-age (~10-500 Myr) L-type dwarfs remains unknown. It has been suggested that low-gravity atmospheres containing large amounts of ...dust may account for the observed reddish nature. We explored an alternative scenario by simulating debris disc around G 196-3 B, which is an L3 young brown dwarf with a mass of ~15 M sub( Jup) and an age in the interval 20-300 Myr. The best-fit solution to G 196-3 B's photometric spectral energy distribution from optical wavelengths through 24 ...m corresponds to the combination of an unreddened L3 atmosphere (T sub( eff) ... 1870 K) and a warm (...1280 K), narrow (...0.07-0.11 R...) debris disc located at very close distances (...0.12-0.20 R...) from the central brown dwarf. This putative, optically thick, dusty belt, whose presence is compatible with the relatively young system age, would have a mass greater than or equal to 7 x 10 super( -10) M... comprised of submicron/micron characteristic dusty particles with temperatures close to the sublimation threshold of silicates. Considering the derived global properties of the belt and the disc-to-brown dwarf mass ratio, the dusty ring around G 196-3 B may resemble the rings of Neptune and Jupiter, except for its high temperature and thick vertical height (...6 x 10 super( 3) km). Our inferred debris disc model is able to reproduce G 196-3 B's spectral energy distribution to a satisfactory level of achievement. (ProQuest: ... denotes formulae/symbols omitted.)
Aims.
We aim to detect planetary companions to young stars with debris disks via the radial velocity method.
Methods.
We observed HD 114082 during April 2018–August 2022 as one of the targets of our ...RVSPY program (Radial Velocity Survey for Planets around Young stars). We use the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs). Additionally, we analyze archival HARPS spectra and TESS photometric data. We use the CERES, CERES++ and SERVAL pipelines to derive RVs and activity indicators and ExoStriker for the independent and combined analysis of the RVs and TESS photometry.
Results.
We report the discovery of a warm super-Jovian companion around HD 114082 based on a 109.8±0.4 day signal in the combined RV data from FEROS and HARPS, and on one transit event in the TESS photometry. The best-fit model indicates a 8.0±1.0
M
Jup
companion with a radius of 1.00±0.03
R
Jup
in an orbit with a semi-major axis of 0.51±0.01 au and an eccentricity of 0.4±0.04. The companions orbit is in agreement with the known near edge-on debris disk located at ∼28 au. HD 114082 b is possibly the youngest (15±6 Myr), and one of only three young (< 100 Myr) giant planetary companions for which both their mass and radius have been determined observationally. It is probably the first properly model-constraining giant planet that allows distinguishing between hot and cold-start models. It is significantly more compatible with the cold-start model.
Context.
The occurrence rate and period distribution of (giant) planets around young stars is still not as well constrained as for older main-sequence stars. This is mostly due to the intrinsic ...activity-related complications and the avoidance of young stars in many large planet search programmes. Yet, dynamical restructuring processes in planetary systems may last significantly longer than the actual planet formation phase and may well extend long into the debris disc phase, such that the planet populations around young stars may differ from those observed around main-sequence stars.
Aims.
We introduce our Radial Velocity Survey for Planets around Young stars (RVSPY), which is closely related to the NaCo-ISPY direct imaging survey, characterise our target stars, and search for substellar companions at orbital separations smaller than a few au from the host star.
Methods.
We used the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs) of 111 stars, most of which are surrounded by debris discs. Our target stars have spectral types between early F and late K, a median age of 400 Myr, and a median distance of 45 pc. During the initial reconnaissance phase of our survey, we determined stellar parameters and used high-cadence observations to characterise the intrinsic stellar activity, searched for hot companions with orbital periods of up to 10 days, and derived the detection thresholds for longer-period companions. In our analysis we, have included archival spectroscopic data, spectral energy distribution, and data for photometric time series from the TESS mission.
Results.
For all target stars we determined their basic stellar parameters and present the results of the high-cadence RV survey and activity characterisation. We have achieved a median single-measurement RV precision of 6 m s−1 and derived the short-term intrinsic RV scatter of our targets (median 23 m s−1), which is mostly caused by stellar activity and decays with an age from >100 m s−1 at <20 Myr to <20 m s−1 at >500 Myr. We analysed time series periodograms of the high-cadence RV data and the shape of the individual cross-correlation functions. We discovered six previously unknown close companions with orbital periods between 10 and 100 days, three of which are low-mass stars, and three are in the brown dwarf mass regime. We detected no hot companion with an orbital period <10 days down to a median mass limit of ~1
M
Jup
for stars younger than 500 Myr, which is still compatible with the established occurrence rate of such companions around main-sequence stars. We found significant RV periodicities between 1.3 and 4.5 days for 14 stars, which are, however, all caused by rotational modulation due to starspots. We also analysed the data for TESS photometric time series and found significant periodicities for most of the stars. For 11 stars, the photometric periods are also clearly detected in the RV data. We also derived stellar rotation periods ranging from 1 to 10 days for 91 stars, mostly from the TESS data. From the intrinsic activity-related short-term RV jitter, we derived the expected mass-detection thresholds for longer-period companions, and selected 84 targets for the longer-term RV monitoring.
We study a possibility to detect signatures of brown dwarf companions in a circumstellar disc based on spectral energy distributions (SED). We present the results of SED simulations for a system with ...a 0.8 \(M_{\odot}\) central object and a companion with a mass of 30 \(M_J\) embedded in a typical protoplanetary disc. We use a solution to the one-dimensional radiative transfer equation to calculate the protoplanetary disc flux density and assume, that the companion moves along a circular orbit and clears a gap. The width of the gap is assumed to be the diameter of the brown dwarf Hill sphere. Our modelling shows that the presence of such a gap can initiate an additional minimum in the SED profile of a protoplanetary disc at \(\lambda = 10 - 100\) \(\mu\)m. We show that the depth of this minimum and the wavelength of the maximum difference between the SEDs of the system with and without a companion are related to the companion mass and its proximity to the star. We found that it is possible to detect signatures of the companion when it is located within 10 AU, even when it is as small as 3 \(M_J\). We also analyse how the disc parameters (the inner radius and the temperature profile) change the maximum difference between the SEDs for the same systems with and without a companion. The SED of a protostellar disc with a massive fragment might have a similar double peaked profile to the SED of a more evolved disc that contains a gap. However, in this case, it will be caused by the presence of an additional maximum at shorter wavelengths and will be similar only when the massive fragment is relatively cold (\(\sim\)400 K).
We present the results of a spectroscopic analysis and spectral energy distribution (SED) modelling of the optical counterpart of the infrared source IRAS 22150+6109. The source was suggested to be ...as a Herbig Be star located in the star forming region L 1188. Absorption lines in the optical spectrum indicate a spectral type B3, while weak Balmer emission lines reflect the presence of a circumstellar gaseous disc. The star shows no excess radiation in the near-infrared spectral region and a strong excess in the far-infrared that we interpret as radiation from a large disc, whose inner edge is located very far from the star (550 au) and does not attenuate its radiation. We conclude that IRAS 22150+6109 is an intermediate-mass star that is currently undergoing a short pre-main-sequence evolutionary stage.
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