A VLBI resolution of the Pleiades distance controversy Melis, Carl; Reid, Mark J.; Mioduszewski, Amy J. ...
Science (American Association for the Advancement of Science),
08/2014, Letnik:
345, Številka:
6200
Journal Article
Recenzirano
Because of its proximity and its youth, the Pleiades open cluster of stars has been extensively studied and serves as a cornerstone for our understanding of the physical properties of young stars. ...This role is called into question by the “Pleiades distance controversy,” wherein the cluster distance of 120.2 ± 1.5 parsecs (pc) as measured by the optical space astrometry mission Hipparcos is significantly different from the distance of 133.5 ± 1.2 pc derived with other techniques. We present an absolute trigonometric parallax distance measurement to the Pleiades cluster that uses very long baseline radio interferometry (VLBI). This distance of 136.2 ± 1.2 pc is the most accurate and precise yet presented for the cluster and is incompatible with the Hipparcos distance determination. Our results cement existing astrophysical models for Pleiades-age stars.
We report the detection of V1298 Tau b, a warm Jupiter-sized planet (RP = 0.91 0.05 RJup, P = 24.1 days) transiting a young solar analog with an estimated age of 23 Myr. The star and its planet ...belong to Group 29, a young association in the foreground of the Taurus-Auriga star-forming region. While hot Jupiters have been previously reported around young stars, those planets are non-transiting and near-term atmospheric characterization is not feasible. The V1298 Tau system is a compelling target for follow-up study through transmission spectroscopy and Doppler tomography owing to the transit depth (0.5%), host star brightness (Ks = 8.1 mag), and rapid stellar rotation ( = 23 km s−1). Although the planet is Jupiter-sized, its mass is currently unknown due to high-amplitude radial velocity jitter. Nevertheless, V1298 Tau b may help constrain formation scenarios for at least one class of close-in exoplanets, providing a window into the nascent evolution of planetary interiors and atmospheres.
ABSTRACT We examine the repeatability, reliability, and accuracy of differential exoplanet eclipse depth measurements made using the InfraRed Array Camera (IRAC) on the Spitzer Space Telescope during ...the post-cryogenic mission. We have re-analyzed an existing 4.5 m data set, consisting of 10 observations of the XO-3b system during secondary eclipse, using seven different techniques for removing correlated noise. We find that, on average, for a given technique, the eclipse depth estimate is repeatable from epoch to epoch to within 156 parts per million (ppm). Most techniques derive eclipse depths that do not vary by more than a factor 3 of the photon noise limit. All methods but one accurately assess their own errors: for these methods, the individual measurement uncertainties are comparable to the scatter in eclipse depths over the 10 epoch sample. To assess the accuracy of the techniques as well as to clarify the difference between instrumental and other sources of measurement error, we have also analyzed a simulated data set of 10 visits to XO-3b, for which the eclipse depth is known. We find that three of the methods (BLISS mapping, Pixel Level Decorrelation, and Independent Component Analysis) obtain results that are within three times the photon limit of the true eclipse depth. When averaged over the 10 epoch ensemble, 5 out of 7 techniques come within 60 ppm of the true value. Spitzer exoplanet data, if obtained following current best practices and reduced using methods such as those described here, can measure repeatable and accurate single eclipse depths, with close to photon-limited results.
We have performed mid-IR photometry of the young open cluster NGC 2264 using the images obtained with the Spitzer Space Telescope Infrared Array Camera and Multiband Imaging Photometer for Spitzer ...instruments and presented a normalized classification scheme of young stellar objects in various color-color diagrams to make full use of the information from multicolor photometry. These results are compared with the classification scheme based on the slope of the spectral energy distribution (SED). From the spatial distributions of Class I and II stars, we have identified two subclusterings of Class I objects in the CONE region of Sung et al. The disked stars in the other star-forming region S Mon are mostly Class II objects. These three regions show a distinct difference in the fractional distribution of SED slopes as well as the mean value of SED slopes. The fraction of stars with primordial disks is nearly flat between log m = 0.2 and -0.5 and that of transition disks is very high for solar mass stars. In addition, we have derived a somewhat higher value of the primordial disk fraction for NGC 2264 members located below the main pre-main-sequence locus (so-called BMS stars). This result supports the idea that BMS stars are young stars with nearly edge-on disks. We have also found that the fraction of primordial disks is very low near the most massive star S Mon and increases with distance from S Mon.
We present a variability analysis of the early-release first quarter of data publicly released by the Kepler project. Using the stellar parameters from the Kepler Input Catalog, we have separated the ...sample into 129,000 dwarfs and 17,000 giants and further sub-divided the luminosity classes into temperature bins corresponding approximately to the spectral classes A, F, G, K, and M. Utilizing the inherent sampling and time baseline of the public data set (30 minute sampling and 33.5 day baseline), we have explored the variability of the stellar sample. The overall variability rate of the dwarfs is 25% for the entire sample, but can reach 100% for the brightest groups of stars in the sample. G dwarfs are found to be the most stable with a dispersion floor of Delta *s ~ 0.04 mmag. At the precision of Kepler, >95% of the giant stars are variable with a noise floor of ~0.1 mmag, 0.3 mmag, and 10 mmag for the G giants, K giants, and M giants, respectively. The photometric dispersion of the giants is consistent with acoustic variations of the photosphere; the photometrically derived predicted radial velocity distribution for the K giants is in agreement with the measured radial velocity distribution. We have also briefly explored the variability fraction as a function of data set baseline (1-33 days), at the native 30 minute sampling of the public Kepler data. To within the limitations of the data, we find that the overall variability fractions increase as the data set baseline is increased from 1 day to 33 days, in particular for the most variable stars. The lower mass M dwarf, K dwarf, and G dwarf stars increase their variability more significantly than the higher mass F dwarf and A dwarf stars as the time baseline is increased, indicating that the variability of the lower mass stars is mostly characterized by timescales of weeks while the variability of the higher mass stars is mostly characterized by timescales of days. A study of the distribution of the variability as a function of galactic latitude suggests that sources closer to the galactic plane are more variable. This may be the result of sampling differing populations (i.e., ages) as a function of latitude or may be the result of higher background contamination that is inflating the variability fractions at lower latitudes. A comparison of the M dwarf statistics to the variability of 29 known bright M dwarfs indicates that the M dwarfs are primarily variable on timescales of weeks or longer presumably dominated by spots and binarity. On shorter timescales of hours, which are relevant for planetary transit detection, the stars are significantly less variable, with ~80% having 12 hr dispersions of 0.5 mmag or less.
A Census of the Young Cluster IC 348 Luhman, K. L; Stauffer, John R; Muench, A. A ...
Astrophysical journal/The Astrophysical journal,
08/2003, Letnik:
593, Številka:
2
Journal Article
The Age of AB Doradus Luhman, K. L; Stauffer, John R; Mamajek, E. E
The Astrophysical journal,
07/2005, Letnik:
628, Številka:
1
Journal Article
Recenzirano
We have derived a new age estimate for the nearby young star AB Dor and have investigated the resulting implications for testing theoretical evolutionary models with the data reported by Close and ...coworkers for the low-mass companion AB Dor C. Using color-magnitude diagrams, we find that the AB Dor moving group is roughly coeval with the Pleiades ( tau = 100-125 Myr) and is clearly older than IC 2391 ( tau = 35-50 Myr). In fact, based on a comparison of the kinematics of AB Dor and the Pleiades, we suggest that the stars identified by Zuckerman and coworkers as members of a moving group with AB Dor are remnants of the large-scale star-formation event that formed the Pleiades. Using the age of tau = 50 super(+) sub(-) super(5) sub(2) super(0) sub(0) Myr adopted by Close, the luminosity predicted by the models of Chabrier and Baraffe for AB Dor C is larger than the value reported by Close but is still within the quoted uncertainties. Meanwhile, the agreement is good when our age estimate for AB Dor C is adopted. Thus, we find no evidence in the data presented by Close for AB Dor C to suggest that previous studies using the models of Chabrier and Baraffe and bolometric luminosity as the mass indicator have significantly underestimated the masses of young low-mass stars and brown dwarfs.
The Metallicity of the Pleiades Soderblom, David R; Laskar, Tanmoy; Valenti, Jeff A ...
The Astronomical journal,
11/2009, Letnik:
138, Številka:
5
Journal Article
Recenzirano
Odprti dostop
We have measured the abundances of Fe, Si, Ni, Ti, and Na in 20 Pleiades stars with T eff values near solar and with low vsin i using high-resolution, high signal-to-noise echelle spectra. We have ...validated our procedures by also analyzing 10 field stars of a range of temperatures and metallicities that were observed by Valenti and Fischer. Our result for the Pleiades is Fe/H = +0.03 +/- 0.02 +/- 0.05 (statistical and systematic). The average of published measurements for the Pleiades is +0.042 +/- 0.021.
We make use of new near- and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to ...define the single-star main-sequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near- and mid-IR photometry extend effectively 2 mag deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low-mass and substellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new candidate members fainter than K sub(s) = 14 (corresponding to 0.1 M unk). These candidate members should eventually allow a better estimate of the cluster mass function to be made down to of order 0.04 M unk. We also use new IRAC data, in particular the images obtained at 8 mu m, in order to comment briefly on interstellar dust in and near the Pleiades. We confirm, as expected, that--with one exception--a sample of low-mass stars recently identified as having 24 urn excesses due to debris disks do not have significant excesses at IRAC wavelengths. However, evidence is also presented that several of the Pleiades high-mass stars are found to be impacting with local condensations of the molecular cloud that is passing through the Pleiades at the current epoch.
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