| 1. |
- Buchhave, Lars A., et al.
(författare)
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An abundance of small exoplanets around stars with a wide range of metallicities
- 2012
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 486:7403, s. 375-377
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Tidskriftsartikel (refereegranskat)abstract
- The abundance of heavy elements (metallicity) in the photospheres of stars similar to the Sun provides a 'fossil' record of the chemical composition of the initial protoplanetary disk. Metal-rich stars are much more likely to harbour gas giant planets(1-4), supporting the model that planets form by accumulation of dust and ice particles(5). Recent ground-based surveys suggest that this correlation is weakened for Neptunian-sized planets(4,6-9). However, how the relationship between size and metallicity extends into the regime of terrestrial-sized exoplanets is unknown. Here we report spectroscopic metallicities of the host stars of 226 small exoplanet candidates discovered by NASA's Kepler mission(10), including objects that are comparable in size to the terrestrial planets in the Solar System. We find that planets with radii less than four Earth radii form around host stars with a wide range of metallicities (but on average a metallicity close to that of the Sun), whereas large planets preferentially form around stars with higher metallicities. This observation suggests that terrestrial planets may be widespread in the disk of the Galaxy, with no special requirement of enhanced metallicity for their formation.
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| 2. |
- Howard, Andrew W., et al.
(författare)
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The California planet survey. I. four new giant exoplanets
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 721:2, s. 1467-1481
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Tidskriftsartikel (refereegranskat)abstract
- We present precise Doppler measurements of four stars obtained during the past decade at Keck Observatory by the California Planet Survey (CPS). These stars, namely, HD 34445, HD 126614, HD 13931, and Gl 179, all show evidence for a single planet in Keplerian motion. We also present Doppler measurements from the Hobby-Eberly Telescope (HET) for two of the stars, HD 34445 and Gl 179, that confirm the Keck detections and significantly refine the orbital parameters. These planets add to the statistical properties of giant planets orbiting near or beyond the ice line, and merit follow-up by astrometry, imaging, and space-borne spectroscopy. Their orbital parameters span wide ranges of planetary minimum mass (M sin i = 0.38-1.9 M-Jup), orbital period (P = 2.87-11.5 yr), semimajor axis (a = 2.1-5.2 AU), and eccentricity (e = 0.02-0.41). HD 34445 b (P = 2.87 yr, M sin i = 0.79 MJup, e = 0.27) is a massive planet orbiting an old, G-type star. We announce a planet, HD 126614 Ab, and an M dwarf, HD 126614 B, orbiting the metal-rich star HD 126614 (which we now refer to as HD 126614 A). The planet, HD 126614 Ab, has minimum mass M sin i = 0.38 MJup and orbits the stellar primary with period P = 3.41 yr and orbital separation a = 2.3 AU. The faint M dwarf companion, HD 126614 B, is separated from the stellar primary by 489 mas (33 AU) and was discovered with direct observations using adaptive optics and the PHARO camera at Palomar Observatory. The stellar primary in this new system, HD 126614 A, has the highest measured metallicity ([ Fe/ H] = + 0.56) of any known planet-bearing star. HD 13931 b (P = 11.5 yr, M sin i = 1.88 MJup, e = 0.02) is a Jupiter analog orbiting a near solar twin. Gl 179 b (P = 6.3 yr, M sin i = 0.82 M-Jup, e = 0.21) is a massive planet orbiting a faint M dwarf. The high metallicity of Gl 179 is consistent with the planet-metallicity correlation among M dwarfs, as documented recently by Johnson & Apps.
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| 3. |
- Howard, Andrew W., et al.
(författare)
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The NASA-UC Eia-earth program. II. a planet orbiting HD 156668 with a minimum mass of four earth masses
- 2011
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 726:2, s. 73-
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of HD 156668 b, an extrasolar planet with a minimum mass of M-P sin i = 4.15 M-circle plus. This planet was discovered through Keplerian modeling of precise radial velocities from Keck-HIRES and is the second super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is consistent with circular and has a period of P = 4.6455 days. The Doppler semi-amplitude of this planet, K = 1.89 m s(-1), is among the lowest ever detected, on par with the detection of GJ 581 e using HARPS. A longer period (P approximate to 2.3 years), low-amplitude signal of unknown origin was also detected in the radial velocities and was filtered out of the data while fitting the short-period planet. Additional data are required to determine if the long-period signal is due to a second planet, stellar activity, or another source. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over the radial velocity period to 0.1 mmag, supporting the existence of the planet. No transits were detected down to a photometric limit of similar to 3 mmag, ruling out transiting planets dominated by extremely bloated atmospheres, but not precluding a transiting solid/liquid planet with a modest atmosphere.
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| 4. |
- Howard, Andrew W., et al.
(författare)
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THE NASA-UC ETA-EARTH PROGRAM : I. A SUPER-EARTH ORBITING HD 7924
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 696:1, s. 75-83
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of the first low-mass planet to emerge from the NASA-UC Eta-Earth Program, a super-Earth orbiting the K0 dwarf HD 7924. Keplerian modeling of precise Doppler radial velocities reveals a planet with minimum mass M-P sin i = 9.26M(circle plus) in a P = 5.398 d orbit. Based on Keck-HIRES measurements from 2001 to 2008, the planet is robustly detected with an estimated false alarm probability of less than 0.001. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 7924 is photometrically constant over the radial velocity period to 0.19 mmag, supporting the existence of the planetary companion. No transits were detected down to a photometric limit of similar to 0.5 mmag, eliminating transiting planets with a variety of compositions. HD 7924b is one of only eight planets detected by the radial velocity technique with M-P sini < 10 M-circle plus and as such is a member of an emerging family of low-mass planets that together constrain theories of planet formation.
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| 5. |
- Howard, Andrew W., et al.
(författare)
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THE NASA-UC ETA-EARTH PROGRAM. III. A SUPER-EARTH ORBITING HD 97658 AND A NEPTUNE-MASS PLANET ORBITING G1 785
- 2011
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 730:1, s. 10-
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of planets orbiting two bright, nearby early K dwarf stars, HD 97658 and G1 785. These planets were detected by Keplerian modeling of radial velocities measured with Keck-HIRES for the NASA-UC Eta-Earth Survey. HD 97658 b is a close-in super-Earth with minimum mass M sin i = 8.2 +/- 1.2 M-circle plus, orbital period P = 9.494 +/- 0.005 days, and an orbit that is consistent with circular. G1 785 b is a Neptune-mass planet with M sin i = 21.6 +/- 2.0 M-circle plus, P = 74.39 +/- 0.12 days, and orbital eccentricity e = 0.30 +/- 0.09. Photometric observations with the T12 0.8 m automatic photometric telescope at Fairborn Observatory show that HD 97658 is photometrically constant at the radial velocity period to 0.09 mmag, supporting the existence of the planet.
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| 6. |
- Fischer, Debra A., et al.
(författare)
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M2K. II. A Triple-Planet System Orbiting Hip 57274
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 745:1, s. 21-
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Tidskriftsartikel (refereegranskat)abstract
- Doppler observations from Keck Observatory have revealed a triple-planet system orbiting the nearby K4V star, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with M sin i = 11.6 M-circle plus (0.036 M-Jup), an orbital period of 8.135 +/- 0.004 days, and slightly eccentric orbit e = 0.19 +/- 0.1. We calculate a transit probability of 6.5% for the inner planet. The second planet has M sin i = 0.4 M-Jup with an orbital period of 32.0 +/- 0.02 days in a nearly circular orbit (e = 0.05 +/- 0.03). The third planet has M sin i = 0.53 M-Jup with an orbital period of 432 +/- 8 days (1.18 years) and an eccentricity e = 0.23 +/- 0.03. This discovery adds to the number of super-Earth mass planets with M sin i < 12 M-circle plus that have been detected with Doppler surveys. We find that 56% +/- 18% of super-Earths are members of multi-planet systems. This is certainly a lower limit because of observational detectability limits, yet significantly higher than the fraction of Jupiter mass exoplanets, 20% +/- 8%, that are members of Doppler-detected, multi-planet systems.
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| 7. |
- Solano, Enrique, et al.
(författare)
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A bright triple transient that vanished within 50 min
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 527:3, s. 6312-6320
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Tidskriftsartikel (refereegranskat)abstract
- We report on three optically bright, ∼16th mag, point sources within 10 arcsec of each other that vanished within 1 h, based on two consecutive exposures at Palomar Observatory on 1952 July 19 (POSS I Red and Blue). The three point sources have continued to be absent in telescope exposures during 71 yr with detection thresholds of ∼21st mag. We obtained two deep exposures with the 10.4-m Gran Telescopio Canarias on 2023 April 25 and 27 in r and g band, both reaching magnitude 25.5 (3σ). The three point sources are still absent, implying they have dimmed by more than 10 mag within an hour back in 1952. When bright in 1952, the most isolated transient source has a profile nearly the same as comparison stars, implying the sources are subarcsec in angular size and they exhibit no elongation due to movement. This triple transient has observed properties similar to other cases where groups of transients ('multiple transients') have appeared and vanished in a small region within a plate exposure. The explanation for these three transients and the previously reported cases remains unclear. Models involving background objects that are optically luminous for less than 1 h coupled with foreground gravitational lensing seem plausible. If so, a significant population of massive objects with structure serving as the lenses, to produce three images, are required to explain the subhour transients.
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| 8. |
- Villarroel, Beatriz, et al.
(författare)
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Exploring nine simultaneously occurring transients on April 12th 1950
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Nine point sources appeared within half an hour on a region within similar to 10 arcmin of a red-sensitive photographic plate taken in April 1950 as part of the historic Palomar Sky Survey. All nine sources are absent on both previous and later photographic images, and absent in modern surveys with CCD detectors which go several magnitudes deeper. We present deep CCD images with the 10.4-m Gran Telescopio Canarias, reaching brightness r similar to 26 mag, that reveal possible optical counterparts, although these counterparts could equally well be just chance projections. The incidence of transients in the investigated photographic plate is far higher than expected from known detection rates of optical counterparts to e.g. flaring dwarf stars, Fast Radio Bursts, Gamma Ray Bursts or microlensing events. One possible explanation is that the plates have been subjected to an unknown type of contamination producing mainly point sources with of varying intensities along with some mechanism of concentration within a radius of similar to 10 arcmin on the plate. If contamination as an explanation can be fully excluded, another possibility is fast (t <0.5 s) solar reflections from objects near geosynchronous orbits. An alternative route to confirm the latter scenario is by looking for images from the First Palomar Sky Survey where multiple transients follow a line.
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| 9. |
- Villarroel, Beatriz, et al.
(författare)
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Launching the VASCO Citizen Science Project
- 2022
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Ingår i: Universe. - : MDPI AG. - 2218-1997. ; 8:11, s. 561-
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Tidskriftsartikel (refereegranskat)abstract
- The Vanishing & Appearing Sources during a Century of Observations (VASCO) project investigates astronomical surveys spanning a time interval of 70 years, searching for unusual and exotic transients. We present herein the VASCO Citizen Science Project, which can identify unusual candidates driven by three different approaches: hypothesis, exploratory, and machine learning, which is particularly useful for SETI searches. To address the big data challenge, VASCO combines three methods: the Virtual Observatory, user-aided machine learning, and visual inspection through citizen science. Here we demonstrate the citizen science project and its improved candidate selection process, and we give a progress report. We also present the VASCO citizen science network led by amateur astronomy associations mainly located in Algeria, Cameroon, and Nigeria. At the moment of writing, the citizen science project has carefully examined 15,593 candidate image pairs in the data (ca. 10% of the candidates), and has so far identified 798 objects classified as "vanished". The most interesting candidates will be followed up with optical and infrared imaging, together with the observations by the most potent radio telescopes.
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