Kapteyn's Star Research Articles

A GALEX Far-ultraviolet Study of Dwarf Stars in Moving Groups

Far-ultraviolet (FUV) GALEX photometry of main-sequence stars in moving groups is used to verify that there is a relationship between age and FUV broadband magnitude among such stars. Samples of dwarf stars were compiled for twelve moving groups and a search made for both GALEX FUV magnitudes on the AB system and Johnson BV photometry. These data sets were used to calculate a (FUV − B) color index for each star, which in turn was plotted against B − V in a two-color diagram. Based on the loci that the group dwarfs define in this two-color space, there is strong evidence that among candidate members of the Hyades, HR 1614, Wolf 630, Ursa Major, Arcturus, AB Doradus, η Cephei, β Pictoris, and Tucana–Horologium moving groups there are populations of coeval stars. Evidence for coevality is weaker in the case of the ζ Herculis group, and no conclusion can be drawn for candidate stars that have previously been assigned to the Kapteyn's Star and σ Puppis groups. Polynomials of up to fifth order were fitted to the two-color loci of the dwarfs in each group. These fits were used to calculate fiducial values of (FUV − B) throughout a range in B − V color on the main sequence for most of the groups studied here. Evidence is found that at a fixed B − V there is a logarithmic dependence of (FUV − B) color on stellar age for FGK dwarfs. The relationships presented herein could potentially serve as a tool for estimating the ages of late-type Population I dwarf stars.

2MASS J06562998+3002455: Not a Cool White Dwarf Candidate, but a Population II Halo Star

2MASS J06562998+3002455 or PSS 309-6 is a high proper-motion star that was discovered during a survey with the 2.1 m telescope at Kitt Peak National Observatory. Here, we reevaluate the status of this interesting star using Gaia DR2. Our results strongly suggest that PSS 309-6 could be a Population II star as the value of its V component is close to -220 km/s, which is typical for halo stars in the immediate solar neighborhood. Kapteyn's star is the nearest known halo star and PSS 309-6 exhibits similar kinematic and photometric signatures. Its properties also resemble those of 2MASS J15484023-3544254, which was once thought to be the nearest cool white dwarf but was later reclassified as K-type subdwarf. Although it is virtually certain that PSS 309-6 is not a nearby white dwarf but a more distant Population II subdwarf, further spectroscopic information, including radial velocity measurements, is necessary to fully characterize this probable member of the Galactic halo.

STELLAR ACTIVITY MIMICS A HABITABLE-ZONE PLANET AROUND KAPTEYN’S STAR

Kapteyn's star is an old M subdwarf believed to be a member of the Galactic halo population of stars. A recent study has claimed the existence of two super-Earth planets around the star based on radial velocity (RV) observations. The innermost of these candidate planets--Kapteyn b (P = 48 days)--resides within the circumstellar habitable zone. Given recent progress in understanding the impact of stellar activity in detecting planetary signals, we have analyzed the observed HARPS data for signatures of stellar activity. We find that while Kapteyn's star is photometrically very stable, a suite of spectral activity indices reveals a large-amplitude rotation signal, and we determine the stellar rotation period to be 143 days. The spectral activity tracers are strongly correlated with the purported RV signal of "planet b," and the 48-day period is an integer fraction (1/3) of the stellar rotation period. We conclude that Kapteyn b is not a planet in the Habitable Zone, but an artifact of stellar activity.

Two planets around Kapteyn's star: a cold and a temperate super-Earth orbiting the nearest halo red dwarf

Abstract Exoplanets of a few Earth masses can be now detected around nearby low-mass stars using Doppler spectroscopy. In this Letter, we investigate the radial velocity variations of Kapteyn's star, which is both a sub-dwarf M-star and the nearest halo object to the Sun. The observations comprise archival and new HARPS (High Accuracy Radial velocity Planet Searcher), High Resolution Echelle Spectrometer (HIRES) and Planet Finder Spectrograph (PFS) Doppler measurements. Two Doppler signals are detected at periods of 48 and 120 d using likelihood periodograms and a Bayesian analysis of the data. Using the same techniques, the activity indices and archival All Sky Automated Survey (ASAS-3) photometry show evidence for low-level activity periodicities of the order of several hundred days. However, there are no significant correlations with the radial velocity variations on the same time-scales. The inclusion of planetary Keplerian signals in the model results in levels of correlated and excess white noise that are remarkably low compared to younger G, K and M dwarfs. We conclude that Kapteyn's star is most probably orbited by two super-Earth mass planets, one of which is orbiting in its circumstellar habitable zone, becoming the oldest potentially habitable planet known to date. The presence and long-term survival of a planetary system seem a remarkable feat given the peculiar origin and kinematic history of Kapteyn's star. The detection of super-Earth mass planets around halo stars provides important insights into planet-formation processes in the early days of the Milky Way.

A study of Kapteyn's star

We present a review of the current knowledge of Kapteyn's Star (KS) - a nearby, low-metallicity M-dwarf, with an eccentric and retrograde Galactic orbit. A brief survey of its spectroscopic properties is provided, together with an analysis of its Galactic orbit in a Galaxy model that incorporates resonances. We propose that KS may have once belonged to a dwarf spheroidal galaxy that merged with the Galaxy, and whose present remnant, if it still exists, is a globular cluster similar to ω Cen.

Abundance Survey of M and K Dwarf Stars

We report the measurement of chemical abundances in 35 low-mass main sequence (M and K dwarf) stars. We have measured the abundance of 12 elements in Kapteyn's Star, a nearby halo M subdwarf. The abundances indicate an iron abundance of [Fe/H] = −0.98, which is about 0.5 dex smaller than that measured in the only previous published measurement using atomic absorption lines. We have measured Fe and Ti abundances in 35 M and K dwarfs with −2.39 ⩽ [Fe/H] ⩽ +0.21 using atomic absorption lines, mostly in the 8000A λ

Chemical abundance analysis of Kapteyn's Star

We report spectral chemical abundances for 12 elements in Kapteyn's Star (HD 33793), a subdwarf M star. We use stellar temperature and gravity parameters derived using the recent interferometric measurement of its radius. We find [Fe/H] = -1.13 ± 0.01, [Ti/H] = -0.90 ± 0.03, and a weighted mean metallicity [M/H] = -0.98 ± 0.10, where the uncertainties in temperature, gravity and microturbulence are included in the latter. This value falls about mid-way between the metallicity found in the only previous high-resolution analysis, [M/H] = -0.55 ± 0.15, and the value derived from low-resolution spectra of TiO and CaH features, [M/H] = -1.5 ± 0.5. It is essentially identical to that found using low-resolution infrared spectra of water lines, [M/H] = -1.0 ± 0.3. This abundance determination for a nearby subdwarf M star using well-determined stellar parameters and a spectrum with a high signal-to-noise ratio will provide an anchor point for abundance studies of similar stars where the situation is not so favourable.

Post-main-sequence and POST red giant branch variables with pulsation periods less than one day

view Abstract Citations (16) References (81) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Post-Main-Sequence and POST Red Giant Branch Variables With Pulsation Periods Less Than One Year Eggen, Olin J. Abstract Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5 to 1 solar mass) pulsators are discussed on the basis of four color and H beta light curves published elsewhere. The post-main-sequence variables, called ultrashort period cepheid (USPC) (delta Sct), pulsate in the fundamental and first harmonic modes of radial pulsation and, in many cases, in nonradial modes. The variables for which photometry allows accurate, luminosity estimates and are known to pulsate simultaneously in the fundamental and first harmonic or in the fundamental mode alone, define a PL relation (MV = -2.80 log P - 0.60, fundamental). It is notable that the slope of this relation is in the range of slopes found for classical cepheids. Accurate V photometry is lacking for many of the variables known as 'anomalous cepheids', but the available data divide them into low mass, pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC (delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, for which accurate photometry is available, give remarkably consistent moduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for the clusters, in which they are blue stragglers similar to SX Phe in Kapteyn's star group. The assumption that the four post-giant branch variables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn's star group and RR Lyr in the Groombridge 1830 group, are physical members of these groups and share their V-velocities, leads to a calibration of the photometry for the derivation of reddening, luminosity, and heavy element abundance of 45 field variables. The resulting reddenings are consistent with values obtained by other methods and the metallicities are consistent with the most accurately available spectroscopic determinations of delta S and of Ca II K. The luminosities of the bulk of the variables confirm Sandage's (1993) relation between MV and (Fe/H). Four or five of the field variables are probably binary, including BB Vir which Kinman & Carreta (1992) have independently noted as double. The PL relation for USPC (delta Sct) variables intersects the horizontal branch (HB) near P = 0.3d and at least two field very short period cepheid (VSPC) (RR Lyr) star, FW Lup (0.484 d) and ST Pic (0.486 d) may be first overtone pulsators of the USPC (delta Sct) variety. A dozen field VSPC (RR Lyr) stars populate a (Fe/H), MV relation with the same slope as the other stars but displaced 0.7 mag toward higher luminosities. The only cluster variable found to populate this diplaced relation is No. 9 in 47 Tuc, although ST Vir, which may be a member of the Arcturus group, should also be considered. The elevated luminosities are unlikely to be caused by either evolution or errors in the photometric indices. A possible source of these apparently young VSPC(RR Lyr) variables with halo metallicity is in second (or third) generation globular clusters formed during an episodic collapse of the galaxy that produced metal poor stars but in a dynamical situation that hastened the disruption of the clusters, currently formed, before the still older globular clusters, created under conditions that have kept them in a more disruptive free environment. Publication: The Astronomical Journal Pub Date: June 1994 DOI: 10.1086/117024 Bibcode: 1994AJ....107.2131E Keywords: Globular Clusters; Main Sequence Stars; Star Distribution; Variable Stars; Radial Velocity; Stellar Magnitude; Astrophysics; STARS: OSCILLATIONS full text sources ADS | data products SIMBAD (98)

Large and kinematically unbiased samples of G and K type stars. I - The dwarfs

view Abstract Citations (59) References (79) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Large and kinematically unbiased samples of G and K type stars. I. The dwarfs. Eggen, O. J. Abstract Four-color, Hβ, and (R,I) photometry has been obtained for some 5000 stars in four kinematically unbiased samples; Bright Star Catalogue ("bright star" sample), South Galactic Pole ("SGP" sample), selected areas at +15° declination ("Griffin" sample), and HD stars with Mphot = 8.5 to 8.6 mag inclusive ("Moore-Paddock-Wayman" or MPW sample). The present discussion involves the little-evolved main-sequence stars which constitute only some 10% of the overall sample. The luminosity and abundance parameters are calibrated with the Hyades supercluster, the Sirius supercluster, the Wolf 630 group, the Arcturus group, and Kapteyn's Star Group. Results of possible interest from the calibrating groups and superclusters are presented. The distributions of the abundances and space motions of the sample stars are discussed. Publication: The Astronomical Journal Pub Date: October 1986 DOI: 10.1086/114226 Bibcode: 1986AJ.....92..910E Keywords: Dwarf Stars; G Stars; K Stars; Main Sequence Stars; Stellar Evolution; Astrometry; Carbon Stars; H Beta Line; M Stars; Star Clusters; Stellar Composition; Stellar Luminosity; Astrophysics full text sources ADS | data products SIMBAD (540) GCPD (1) Related Materials (5) Part 2: 1989PASP..101...45E Part 3: 1989PASP..101...54E Part 4: 1989PASP..101..366E Part 5: 1990PASP..102..242E Part 6: 1990PASP..102..507E

Relativistic and perspective effects in proper motions and radial velocities of stars

The heliocentric motion of stars is investigated by taking into account all effects due to the geometry and due to the finite speed of light. It is shown that the proper motions as given in star catalogues contain the main light retardation term; an additional term of this type modifies Schlesinger's (1917) term but is less significant than a 3rd order perspective term neglected in conventional astrometry. Kapteyn's star serves as a numerical example. The ambiguous relativistic relation between Doppler shifts and radial velocities is discussed and demonstrated in a diagram. The ambiguity is solved with rigorous equations which allow to compute the inertial motion of a star from its proper motion, classical radial velocity, and distance. -

Intermediate-band photometry of late-type stars. V - Calibration of indices

view Abstract Citations (48) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Intermediate-band photometry of late-type stars. V. Calibration of indices. Eggen, O. J. Abstract Additional data for several stellar groups and clusters are used to improve a previously determined provisional relation between M1 photometric index and the parameter /Fe/H/(solar) as well as to test the usefulness of the C1 photometric index for luminosity determinations. The data are for 43 members of the Wolf 630 group, 14 members of the 61 Cygni group, 30 members of the Arcturus group, 14 members of Kapteyn's star groups, and various members of the Hyades, 47 Tuc, NGC2420, Omega Cen, and an anonymous group of subdwarfs. It is found that in general the values of C1 only confirm a giant or dwarf classification without yielding accurate luminosities and that the main contribution of C1 for disk objects is in isolating peculiar stars. The results also indicate that there is a luminosity effect in M1 for the strongest-lined stars and that the values of M1 become distorted, probably by the presence of TiO, for R-I larger than about +0.5 magnitude. An array for interpolating /FE/H/(solar) from (R-I, M1) is constructed by adopting mean values of /Fe/H/(solar) equal to +0.1,-0.35, -0.6, and -1.8 for the Hyades, Wolf 630, Arcturus, and Kapteyn's star groups, respectively. Publication: The Astrophysical Journal Pub Date: May 1978 DOI: 10.1086/156091 Bibcode: 1978ApJ...221..881E Keywords: Abundance; Astronomical Photometry; Late Stars; Star Clusters; Stellar Luminosity; Binary Stars; Calibrating; Globular Clusters; Indexes (Ratios); Stellar Spectrophotometry; Astronomy; Late-Type Stars:Luminosities; Late-Type Stars:Photometry; Photometry:Stellar Groups full text sources ADS | data products SIMBAD (77) GCPD (1) Related Materials (8) Part 1: 1976PASP...88..732E Part 2: 1977ApJ...215..812E Part 3: 1977PASP...89..706E Part 4: 1978ApJS...37..251E Part 6: 1978ApJ...222..191E Part 7: 1978ApJ...222..203E Part 8: 1979ApJ...229..158E Part 9: 1979ApJ...234..168E

Spectroscopic Observations of Late-Type Halo M Dwarfs

In the lower main sequence, the coolest halo population stars do not appear to be particularly subluminous in either the standard HR diagram or the (MI, R-I) plane. Earlier type M subdwarf's (e.g., Kapteyn's Star) that lie one or more magnitudes below the main sequence exhibit enhanced hydride absorption bands relative to M dwarfs of the same temperature. From visual region (4500–7000 Å) low dispersion image tube spectrograms we find that the cool halo M dwarfs exhibit enhanced absorption in the CaOH 5530 Å band and Na I resonance lines. Easily noticeable changes in the strength of the CaH “B” band relative to that of the TiO bands was found to be more difficult to determine in halo dwarfs later than spectral type M4. Several M dwarfs with old disk type motions have spectral peculiarities similar to those of the halo dwarfs. In both cases, Balmer emission is not present in most stars, in the rest it is very weak. Therefore, the anomalous strength of the CaOH 5530 Å band and Na resonance lines appear to be a more conveniently utilized qualitative criterion in spectroscopically identifying very cool M dwarfs which are subluminous with respect to most main sequence stars of the same temperature class.

The composition of Kapteyn's star and the M subdwarfs.

view Abstract Citations (53) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The composition of Kapteyn's star and the M subdwarfs. Mould, J. R. Abstract The metal abundance of the nearby M subdwarf Kapteyn's star is obtained from a 10 A mm -1 spectrum in the near-infrared. The weighted mean value of [M/H] is - 0.55 + 0.15 (p.e.), confirming an earlier estimate from the strength of the TiO bands. The 0/C ratio in Kapteyn's star is within a factor of 2 of the solar value. The effect of pressure broadening in a cool subdwarf atmosphere is to strengthen the lines of the Ca ii infrared triplet relative to those of a mainsequence star of equal temperature. Subject headings: stars: abundances - stars: atmospheres - stars: individual - stars: late-type - stars: subdwarfs Publication: The Astrophysical Journal Pub Date: December 1976 DOI: 10.1086/154843 Bibcode: 1976ApJ...210..402M full text sources ADS | data products SIMBAD (31)

The temperature, luminosity and spectrum of Kapteyn's star.

The spectrum of Kapteyn's star has been observed in the blue and red regions with an objective prism. There is no obvious weakening of the atomic lines, but the TiO bands are weak for the atomic-line strength, while the bands of MgH and CaH are greatly enhanced relative to their strength in normal early M dwarfs. Although the metal abundance of Kapteyn's star cannot be determined from the present data, its TiO and CaH band strengths are found to be fairly reliable indicators of its temperature and luminosity, respectively. (AIP)