PDS 70
PDS 70 (V1032 Centauri) is a very young T Tauri star in the constellation Centaurus. Located 370 light-years (110 parsecs) from Earth, it has a mass of 0.76 M☉ and is approximately 5.4 million years old.[3] The star has a protoplanetary disk containing two nascent exoplanets, named PDS 70b and PDS 70c, which have been directly imaged by the European Southern Observatory's Very Large Telescope. PDS 70b was the first confirmed protoplanet to be directly imaged.[6][7][3]
The protoplanetary disk of PDS 70 with new planet PDS 70b (right) | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Centaurus |
| Right ascension | 14h 08m 10.15455s[1] |
| Declination | −41° 23′ 52.5733″[1] |
| Apparent magnitude (V) | 12[2] |
| Characteristics | |
| Evolutionary stage | Pre-main-sequence (T Tauri) |
| Spectral type | K7[3] |
| U−B color index | 0.71[4] |
| B−V color index | 1.06[4] |
| Astrometry | |
| Radial velocity (Rv) | 0.74±3.22[1] km/s |
| Proper motion (μ) | RA: -29.697 mas/yr[1] Dec.: -24.041 mas/yr[1] |
| Parallax (π) | 8.8975 ± 0.0191 mas[1] |
| Distance | 366.6 ± 0.8 ly (112.4 ± 0.2 pc) |
| Details | |
| Mass | 0.76 ± 0.02[3] M☉ |
| Radius | 1.26 ± 0.15[3] R☉ |
| Luminosity | 0.35 ± 0.09[3] L☉ |
| Temperature | 3972 ± 36[3] K |
| Rotation | ~50 days[5] |
| Rotational velocity (v sin i) | ~10[5] km/s |
| Age | 5.4 ± 1[3] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Discovery and naming edit
The "PDS" in this star's name stands for Pico dos Dias Survey, a survey that looked for pre-main-sequence stars based on the star's infrared colors measured by the IRAS satellite.[9] PDS 70 was identified as a T Tauri variable star in 1992, from these infrared colors.[10] PDS 70's brightness varies quasi-periodically with an amplitude of a few hundredths of a magnitude in visible light.[11] Measurements of the star's period in the astronomical literature are inconsistent, ranging from 3.007 days to 5.1 or 5.6 days.[12][13]
Protoplanetary disk edit
The protoplanetary disk around PDS 70 was first hypothesized in 1992[14] and fully imaged in 2006 with phase-mask coronagraph on the VLT.[2] The disk has a radius of approximately 140 au. In 2012 a large gap (~65 au) in the disk was discovered, which was thought to be caused by planetary formation.[5][15]
The gap was later found to have multiple regions: large dust grains were absent out to 80 au, while small dust grains were only absent out to the previously-observed 65 au. There is an asymmetry in the overall shape of the gap; these factors indicate that there are likely multiple planets affecting the shape of the gap and the dust distribution.[16]
The James Webb Space Telescope has been used to detect water vapor in the inner part of the disk, where terrestrial planets may be forming.[17][18]
Planetary system edit
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (years) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 3.2+3.3 −1.6 MJ | 20.8+0.6 −0.7 | 123.5+9.8 −4.9[20] | 0.17±0.06 | 131.0+2.9 −2.6° | 2.72+0.39 −0.34[21] RJ |
| c | 7.5+4.7 −4.2 MJ | 34.3+2.2 −1.8 | 191.5+15.8 −31.5[20] | 0.037+0.041 −0.025 | 130.5+2.5 −2.4° | 2.04+1.22 −0.89[21] RJ |
| Protoplanetary disk | ~65–140 AU | ~130° | — | |||
In results published in 2018, a planet in the disk, named PDS 70 b, was imaged with SPHERE planet imager at the Very Large Telescope (VLT).[3][7] With a mass estimated to be a few times greater than Jupiter,[19] the planet is thought to have a temperature of around 1,200 K (930 °C; 1,700 °F)[21] and an atmosphere with clouds;[7] its orbit has an approximate radius of 20.8 AU (3.11 billion kilometres),[19] taking around 120 years for a revolution.[20]
The emission spectrum of the planet PDS 70 b is gray and featureless, and no molecular species were detected by 2021.[22]
A second planet, named PDS 70 c, was discovered in 2019 using the VLT's MUSE integral field spectrograph.[23] The planet orbits its host star at a distance of 34.3 AU (5.13 billion kilometres), farther away than PDS 70 b.[19] PDS 70 c is in a near 1:2 orbital resonance with PDS 70 b, meaning that PDS 70 c completes nearly one revolution once every time PDS 70 b completes nearly two.[23]
Circumplanetary disks edit
Modelling predicts that PDS 70 b has acquired its own accretion disk.[6][24] The accretion disk was observationally confirmed in 2019,[25] and the accretion rate was measured to be at least 5*10−7 Jupiter masses per year.[26] A 2021 study with newer methods and data suggested a lower accretion rate of 1.4±0.2*10−8 MJ/year.[27]
It is not clear how to reconcile these results with each other and with existing planetary accretion models; future research in accretion mechanisms and Hα emissions production should offer clarity.[28]
The optically thick accretion disk radius is 3.0±0.2 RJ, significantly larger than the planet itself. Its bolometric temperature is 1193±20 K.[29]
In July 2019, astronomers using the Atacama Large Millimeter Array (ALMA) reported the first-ever detection of a moon-forming circumplanetary disk. The disk was detected around PDS 70 c, with a potential disk observed around PDS 70 b.[30][31][32] The disk was confirmed by Caltech-led researchers using the W. M. Keck Observatory in Mauna Kea, whose research was published in May 2020.[33] An image of the circumplanetary disk around PDS 70 c was published in November 2021.[34]
Possible co-orbital body edit
In July 2023, the likely detection of a cloud of debris co-orbital with the planet PDS 70 b was announced. This debris is thought to have a mass 0.03-2 times that of the Moon, and could be evidence of a Trojan planet or one in the process of forming.[35][36]
Gallery edit
- ALMA image of a resolved circumplanetary disk around exoplanet PDS 70c
- Hubble image of PDS 70. This is only the second multi-planet system to be directly imaged.
- James Webb Space Telescope spectrum of PDS 70, detecting water in the terrestrial region of the protoplanetary disk
See also edit
References edit
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- ^ a b c Hashimoto, J.; et al. (2012). "Polarimetric Imaging of Large Cavity Structures in the Pre-Transitional Protoplanetary Disk Around PDS 70: Observations of the Disk". The Astrophysical Journal. 758 (1): L19. arXiv:1208.2075. Bibcode:2012ApJ...758L..19H. doi:10.1088/2041-8205/758/1/L19. S2CID 13691976.
- ^ a b Staff (2 July 2018). "First confirmed image of newborn planet caught with ESO's VLT - Spectrum reveals cloudy atmosphere". EurekAlert!. Retrieved 2 July 2018.
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- ^ Hashimoto, Jun; Aoyama, Yuhiko; Konishi, Mihoko; Uyama, Taichi; Takasao, Shinsuke; Ikoma, Masahiro; Tanigawa, Takayuki (2020). "Accretion Properties of PDS 70b with MUSE". The Astronomical Journal. 159 (5): 222. arXiv:2003.07922. Bibcode:2020AJ....159..222H. doi:10.3847/1538-3881/ab811e. S2CID 212747630.
- ^ Zhou, Yifan; Bowler, Brendan P.; Wagner, Kevin R.; Schneider, Glenn; Apai, Dániel; Kraus, Adam L.; Close, Laird M.; Herczeg, Gregory J.; Fang, Min (2021), "Hubble Space Telescope UV and Hα Measurements of the Accretion Excess Emission from the Young Giant Planet PDS 70 B", The Astronomical Journal, 161 (5): 244, arXiv:2104.13934, Bibcode:2021AJ....161..244Z, doi:10.3847/1538-3881/abeb7a, S2CID 233443901
- ^ Gebhardt, Chris; Warren, Haygen (2021-05-13). "With Hubble, astronomers use UV light for first time to measure a still-forming planet's growth rate". NSF (NASASpaceflight).
...and that's lower than super-Jupiter gas giant planet formation models predict. Zhou et al. are quick to caution that their calculations are a snapshot in time. Additional observation, multi-decade, multi-century observations will reveal if accretion rates fluctuate greatly over time as planets go through growth spurts, so to speak, followed by periods of less active formation or if "Hα production in planetary accretion shocks is more efficient than [previous] models predicted, or [if] we underestimated the accretion luminosity/rate," noted Zhou et al. in their paper published in April 2021 issue of The Astronomical Journal. The team further noted, "By combining our observations with planetary accretion shock models that predict both UV and Hα flux, we can improve the accretion rate measurement and advance our understanding of the accretion mechanisms of gas giant planets."
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