Kappa Andromedae b

Last updated
Kappa Andromedae b
HR 8976 exoplanet.jpg
Kappa Andromedae b is visible as the white blob in the upper left.
Orbital characteristics
57–133 [1] AU
Eccentricity 0.69–0.85 [1]
242–900 [1] y
Inclination 114.9–140 [1]
60.3–90.5 [1]
2038.4–2047.9 [1]
96.6–155.4 [1]
Star Kappa Andromedae
Physical characteristics
Mass 13+12
−2
[2] MJ
Temperature 1,700–2,000  K [2] [3]

    Kappa Andromedae b [4] is a directly imaged substellar object and likely superjovian-mass planet orbiting Kappa Andromedae, a young B9IV star in the Andromeda constellation, about 170 light-years away. [5] The companion's mass is roughly 13 times the mass of Jupiter. [2] As early history on Kappa And b is filled with debate over whether it is an exoplanet or a brown dwarf, some scientists have broadly described it as a "super-Jupiter" object.

    Contents

    Discovery

    Kappa Andromedae b was discovered through near-infrared high-contrast imaging during the Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS) survey at the Subaru Telescope, located atop Mauna Kea, Hawaii. [6] Follow-up Subaru observations taken between January and July 2012 and covering a wider wavelength range confirmed that Kappa Andromedae is gravitationally bound (not a background star) and had infrared colors consistent with a substellar (possibly planet–mass) companion. [6]

    Atmosphere and orbital properties

    The low resolution near-infrared spectrum of Kappa And b, obtained by extreme adaptive optics system SCExAO with the CHARIS integral field spectrograph, is shaped by broad water and carbon monoxide absorption features. [2] Moderate resolution Keck/OSIRIS spectroscopy resolve these lines. [7] Based on comparisons to large libraries of spectra for other substellar objects, the companion likely has a spectral type of L0-L1: its sharp H-band (1.65 microns) shape is indicative of low surface gravity. [1] [2]

    Empirical comparisons to well-characterized substellar objects suggest an effective temperature of 1,700–2,000  K . [2] Atmospheric modeling incorporating longer wavelength data favors the cooler end of this temperature range, while temperatures derived from Keck/OSIRIS spectra favor higher values of 1,950–2,100 K. [7] The atmosphere of Kappa And b is likely filled by thick cloud deck extending to low atmospheric pressures. [1] [3] Analysis of the companion's spectrum yields a near-solar carbon-to-oxygen ratio (C/O ~ 0.70). [7]

    Kappa Andromedae b was first imaged at a projected separation of about 55  AU ; subsequent data sets recover the companion at smaller angular separations. [1] While only a small portion of the companion's orbital phase has been covered, [8] current limits suggest a semimajor axis likely greater than 75 AU. [2] Its eccentricity is fairly high (e ~ 0.7 or greater). [1] The relative radial-velocity between it and its host star is −1.4 +/− 0.9 km/s. [7]

    System age and mass

    The masses of directly imaged substellar objects (exoplanets and brown dwarfs) are usually not directly measured but are instead inferred by comparing their luminosities to predicted values for substellar evolution models. Thus, uncertainties in the system age translate into uncertainties in the object's mass. The discovery paper for Kappa Andromedae b [4] argued that the primary's kinematics are consistent with membership in the Columba association, which would imply a system age of 20 to 50 million years and a mass of about 12.8 Jupiter masses. These results were later questioned [9] [10] by those who argued that the primary star's position on the Hertzsprung–Russell diagram favors a much older age of 220 ± 100 million years, provided that the star, Kappa Andromedae A, is not a fast rotator viewed pole-on. Direct measurements of the star later showed that Kappa Andromedae A is in fact a rapid rotator viewed pole-on [11] and yield a best-estimated age of 47+27
    40
    million years favoring a mass between 13 and 30 jovian masses. A revised luminosity and detailed empirical comparisons with other substellar objects with known ages favor a mass of 13+12
    2
    Jupiter masses. [2]

    Classification and formation

    The nature of Kappa Andromedae b has been long-debated, specifically whether it is a gas giant planet or a brown dwarf, an object massive enough to fuse deuterium but not protium. The Working Group on Extrasolar Planets of the International Astronomical Union adopted the deuterium-burning limit (set at 13 Jupiter masses) to separate planets (below this limit) and brown dwarfs (above it). [12] However, later work has revealed many free-floating objects labeled as brown dwarfs but with inferred masses at or well below the deuterium-burning limit. [13] Models indicate that the exact definition of the deuterium-burning further depends on the assumed metallicity of the object and the completeness of deuterium burning, ranging from 11 Jupiter masses for an extremely metal-rich object at 10% burning to over 16 Jupiter masses for a metal poor object burning 90% of its deuterium. [14] Alternate criteria for separating planets from brown dwarfs abandon the deuterium-burning limit altogether, instead inferring an object's nature based on its mass ratio with respect to its primary and its separation. [15]

    Previous debate centered largely on the system age, since it determines inferred values for the companion mass and mass ratio with respect to its primary star. For the now-disfavored older age (220 ± 100 million years), the inferred mass of the companion would be well above the deuterium-burning limit and its mass ratio would exceed 1%, best consistent with a brown dwarf. Younger ages inferred from possible membership in the Columba association, derived from direct measurements of the star, and consistent with Kappa And b's spectral properties strongly favor masses near 13 Jupiter masses and a mass ratio below 1%. [2] The companion's orbital plane may also be aligned with the rotation axis of the star. These lines of evidence support the classification of this object as a superjovian-mass planet.

    Forming a planet in situ with Kappa And b's properties is extremely challenging for standard core accretion models for jovian planet formation. Instead, planet formation by gravitational instability may be a viable mechanism for this companion. [2] [16] The companion's derived carbon to oxygen ratio, thought to be a diagnostic of the object's accretion environment, and the primary's subsolar metallicity may be evidence that Kappa And b formed through a rapid formation process, like gravitational instability. [7]

    Related Research Articles

    <span class="mw-page-title-main">Brown dwarf</span> Type of substellar object larger than a planet

    Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars. Their mass is approximately 13 to 80 times that of Jupiter (MJ)—not big enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in their cores, but massive enough to emit some light and heat from the fusion of deuterium (2H). The most massive ones can fuse lithium (7Li).

    <span class="mw-page-title-main">2M1207</span> Brown dwarf in the constellation Centaurus

    2M1207, 2M1207A or 2MASS J12073346–3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary-mass companion to be directly imaged, and is the first discovered orbiting a brown dwarf.

    <span class="mw-page-title-main">Gliese 229</span> Star in the constellation Lepus

    Gliese 229 is a binary system composed of a red dwarf and the second brown dwarf seen by astronomers, 18.8 light years away in the constellation Lepus. The primary component has 58% of the mass of the Sun, 69% of the Sun's radius, and a very low projected rotation velocity of 1 km/s at the stellar equator.

    <span class="mw-page-title-main">2M1207b</span> Planetary-mass object orbiting the brown dwarf 2M1207

    2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth. It is one of the first candidate exoplanets to be directly observed. It was discovered in April 2004 by the Very Large Telescope (VLT) at the Paranal Observatory in Chile by a team from the European Southern Observatory led by Gaël Chauvin. It is believed to be from 5 to 6 times the mass of Jupiter and may orbit 2M1207 at a distance roughly as far from the brown dwarf as Pluto is from the Sun.

    <span class="mw-page-title-main">Kappa Andromedae</span> Star in the constellation of Andromeda

    Kappa Andromedae, Latinized from κ Andromedae, is the Bayer designation for a bright star in the northern constellation of Andromeda. It is visible to the naked eye with an apparent visual magnitude of 4.1. Based on the star's ranking on the Bortle Dark-Sky Scale, it is luminous enough to be visible from the suburbs and from urban outskirts, but not from brightly lit inner city regions. Parallax measurements made during the Hipparcos mission place it at a distance of approximately 168 light-years from the Sun. It is drifting closer with a radial velocity of −15 km/s, and there is a high likelihood (86%) that it is a member of the Beta Pictoris moving group. The star has one known companion exoplanet, Kappa Andromedae b.

    <span class="mw-page-title-main">Sub-brown dwarf</span> Astronomical objects of planetary size that did not form in orbit around a star

    A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object that formed in the same manner as stars and brown dwarfs but that has a planetary mass, therefore by definition below the limiting mass for thermonuclear fusion of deuterium . Some researchers call them rogue planets whereas others call them planetary-mass brown dwarfs.

    <span class="mw-page-title-main">AB Pictoris</span> Star in the constellation Pictor

    AB Pictoris is a K-type main-sequence star, located 163.5 light-years away in the southern constellation of Pictor. It has been identified as a member of the young Tucana–Horologium association. The star has been classified as a BY Draconis variable, indicating it has an active chromosphere. It is an X-ray source and displays emission lines in its spectrum.

    <span class="mw-page-title-main">14 Herculis b</span> Extrasolar planet in the constellation Hercules

    14 Herculis b or 14 Her b is an exoplanet approximately 58.4 light-years away in the constellation of Hercules. The planet was found orbiting the star 14 Herculis, with a mass that would make the planet a Jovian planet roughly the same size as Jupiter but much more massive. It was discovered in July 1998 by the Geneva Extrasolar Planet Search team. The discovery was formally published in 2003. At the time of discovery it was the extrasolar planet with the longest orbital period, though longer-period planets have subsequently been discovered.

    <span class="mw-page-title-main">XO-3b</span> Extrasolar planet in the constellation Camelopardalis

    XO-3b is an exoplanet with about 11.79 times the mass of Jupiter, and it orbits its parent star XO-3 in about 3.2 days. The radius of this object is 1.217 times that of Jupiter. Astronomers announced their discovery on May 30, 2007, at the American Astronomical Society in Honolulu, Hawaii. Its discovery is attributed to the combined effort of amateur and professional astronomers working together on the XO Project using a telescope located on the Haleakala summit in Hawaii.

    <span class="mw-page-title-main">HD 136118</span> Star in the constellation Serpens

    HD 136118 is a star in the Serpens Caput section of the Serpens constellation. The star is too dim to be readily visible to the naked eye, having an apparent visual magnitude of 6.93. It is located at a distance of 165 light years from the Sun based on parallax, and is drifting closer with a radial velocity of −3 km/s.

    A substellar object, sometimes called a substar, is an astronomical object, the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained. This definition includes brown dwarfs and former stars similar to EF Eridani B, and can also include objects of planetary mass, regardless of their formation mechanism and whether or not they are associated with a primary star.

    36 Ursae Majoris is a double star in the northern constellation of Ursa Major. With an apparent visual magnitude of 4.8, it can be seen with the naked eye in suitable dark skies. Based upon parallax measurements, this binary lies at a distance of 42 light-years from Earth.

    HD 16760 is a binary star system approximately 227 light-years away in the constellation Perseus. The primary star HD 16760 is a G-type main sequence star similar to the Sun. The secondary, HIP 12635 is 1.521 magnitudes fainter and located at a separation of 14.6 arcseconds from the primary, corresponding to a physical separation of at least 660 AU. Announced in July 2009, HD 16760 has been confirmed to have a red dwarf orbiting it, formerly thought to be a brown dwarf or exoplanet.

    <span class="mw-page-title-main">Gliese 758</span> Star in the constellation Lyra

    Gliese 758 is a star in the northern constellation of Lyra. At about magnitude 6 it is a challenge to view with the naked eye even in good seeing conditions, but can be easily seen through a small telescope or binoculars. Parallax measurements from the Hipparcos mission give it an estimated distance of around 50.9 light-years from Earth.

    HD 175167 b is an exoplanet orbiting HD 175167, which is a G type star within the Pavo constellation 232 light-years away from the Earth. The planet was discovered by the Magellan Planet Search Program as the astronomical object fit the Keplerian orbital model. During the observations 13 doppler velocity tests were conducted, which showed this object's mass was at least 7.8 Jovian-masses and its orbit has a high eccentricity. The exoplanet takes 3.53 years to complete a full stellar orbit.

    <span class="mw-page-title-main">Planetary-mass object</span> Size-based definition of celestial objects

    A planetary-mass object (PMO), planemo, or planetary body is, by geophysical definition of celestial objects, any celestial object massive enough to achieve hydrostatic equilibrium, but not enough to sustain core fusion like a star.

    Deuterium fusion, also called deuterium burning, is a nuclear fusion reaction that occurs in stars and some substellar objects, in which a deuterium nucleus (deuteron) and a proton combine to form a helium-3 nucleus. It occurs as the second stage of the proton–proton chain reaction, in which a deuteron formed from two protons fuses with another proton, but can also proceed from primordial deuterium.

    References

    1. 1 2 3 4 5 6 7 8 9 10 11 Uyama, Taichi; et al. (2020), "Atmospheric Characterization and Further Orbital Modeling of κ Andromeda b", The Astrophysical Journal, 159 (2): 40, arXiv: 1810.09457 , Bibcode:2020AJ....159...40U, doi: 10.3847/1538-3881/ab5afa , S2CID   208248220 }
    2. 1 2 3 4 5 6 7 8 9 10 Currie, Thayne; et al. (2018), "SCExAO/CHARIS Near-infrared Direct Imaging, Spectroscopy, and Forward-Modeling of κ And b: A Likely Young, Low-gravity Superjovian Companion", The Astrophysical Journal, 156 (6): 291, arXiv: 1810.09457 , Bibcode:2018AJ....156..291C, doi: 10.3847/1538-3881/aae9ea , S2CID   119261709 }
    3. 1 2 Stone, Jordan M.; Barman, Travis; Skemer, Andrew J.; Briesemeister, Zackery W.; Brock, Laci S.; Hinz, Philip M.; Leisenring, Jarron M.; Woodward, Charles E.; Skrutskie, Michael F.; Spalding, Eckhart (2020), "High-contrast Thermal Infrared Spectroscopy with ALES: The 3–4 μm Spectrum of κ Andromedae B", The Astronomical Journal, 160 (6): 262, arXiv: 2010.02928 , Bibcode:2020AJ....160..262S, doi: 10.3847/1538-3881/abbef3 , S2CID   222177297
    4. 1 2 Carson; Thalmann; Janson; Kozakis; Bonnefoy; Biller; Schlieder; Currie; McElwain (November 15, 2012). "Direct Imaging Discovery of a 'Super-Jupiter' Around the late B-Type Star Kappa And". The Astrophysical Journal. 763 (2): L32. arXiv: 1211.3744 . Bibcode:2013ApJ...763L..32C. doi:10.1088/2041-8205/763/2/L32. S2CID   119253577.
    5. "Super-Jupiter Kappa Andromedae b: NASA not certain if new discovery is a planet or dwarf star". wptv.com. November 20, 2012. Archived from the original on October 24, 2013. Retrieved November 21, 2012.
    6. 1 2 "Astronomers Directly Image Massive Star's 'Super-Jupiter'". nasa.gov. November 19, 2012. Retrieved November 21, 2012.
    7. 1 2 3 4 5 Wilcomb, K; et al. (2020), "Moderate-resolution K-band Spectroscopy of Substellar Companion κ Andromedae b", The Astrophysical Journal, 160 (5): 207, arXiv: 1810.09457 , Bibcode:2020AJ....160..207W, doi: 10.3847/1538-3881/abb9b1 , S2CID   221802366 }
    8. Blunt, Sarah; et al. (2017). "Orbits for the Impatient: A Bayesian Rejection-sampling Method for Quickly Fitting the Orbits of Long-period Exoplanets". The Astronomical Journal. 153 (5). 229. arXiv: 1703.10653 . Bibcode:2017AJ....153..229B. doi: 10.3847/1538-3881/aa6930 . S2CID   119223138.
    9. Montet, Ben (2013-09-20). "How Massive is Kappa Andromedae B?". Astrobites.
    10. Sasha Hinkley; Laurent Pueyo; Jacqueline K. Faherty; Ben R. Oppenheimer; Eric E. Mamajek; Adam L. Kraus; Emily L. Rice; Michael J. Ireland; Trevor David; et al. (September 2013). "The Kappa Andromedae System: New Constraints on the Companion Mass, System Age & Further Multiplicity". The Astrophysical Journal. 763 (2): L32. arXiv: 1211.3744 . Bibcode:2013ApJ...763L..32C. doi:10.1088/2041-8205/763/2/L32. S2CID   119253577.
    11. Jones, Jeremy; White, R. J.; Quinn, S.; Ireland, M.; Boyajian, T.; Schaefer, G.; Baines, E. K. (2016). "The Age of the Directly Imaged Planet Host Star κ Andromedae Determined from Interferometric Observations". The Astrophysical Journal Letters. 822 (1): 7. arXiv: 1604.02176 . Bibcode:2016ApJ...822L...3J. doi: 10.3847/2041-8205/822/1/L3 . S2CID   38367518.
    12. Boss, Alan P; Butler, R. Paul; Hubbard, William B; Ianna, Philip A; Kürster, Martin; Lissauer, Jack J; Mayor, Michel; Meech, Karen J; Mignard, Francois; Penny, Alan J; Quirrenbach, Andreas; Tarter, Jill C; Vidal-Madjar, Alfred (2007). "Definition of a planet". Proceedings of the International Astronomical Union. 1: 183–186. Bibcode:2007IAUTA..26..183B. doi: 10.1017/S1743921306004509 .
    13. Luhman, K. L. (21 April 2014). "Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun". The Astrophysical Journal Letters . 786 (2): L18. arXiv: 1404.6501 . Bibcode:2014ApJ...786L..18L. doi:10.1088/2041-8205/786/2/L18. S2CID   119102654.
    14. Spiegel, David S.; Burrows, Adam; Milson, John A. (2011). "The Deuterium-Burning Mass Limit for Brown Dwarfs and Giant Planets". The Astrophysical Journal. 727 (1): 57. arXiv: 1008.5150 . Bibcode:2011ApJ...727...57S. doi:10.1088/0004-637X/727/1/57. S2CID   118513110.
    15. Kratter, Kaitlin; et al. (2010). ""The Runts of the Litter: Why planets formed through gravitational instability can only be failed binary stars"". The Astrophysical Journal. 710 (2): 1375. arXiv: 0909.2644 . Bibcode:2010ApJ...710.1375K. doi:10.1088/0004-637X/710/2/1375. S2CID   15653051.
    16. Mickael Bonnefoy; Thayne Currie; G.-D. Marleau; et al. (August 2013). "Characterization of the gaseous companion κ Andromedae b: New Keck and LBTI high-contrast observations". Astronomy & Astrophysics. 562: A111. arXiv: 1308.3859 . Bibcode:2014A&A...562A.111B. doi:10.1051/0004-6361/201322119. S2CID   51944782.