The nature and origin of free-floating planets (FFPs) are still largely unconstrained because of a lack of large homogeneous samples to enable a statistical analysis of their properties. So far, most FFPs have been discovered using indirect methods; microlensing surveys have proved particularly successful to detect these objects down to a few Earth masses. However, the ephemeral nature of microlensing events prevents any follow-up observations and individual characterization. Several studies have identified FFPs in young stellar clusters and the Galactic field but their samples are small or heterogeneous in age and origin. Here we report the discovery of between 70 and 170 FFPs (depending on the assumed age) in the region encompassing Upper Scorpius and Ophiuchus, the closest young OB association to the Sun. We found an excess of FFPs by a factor of up to seven compared with core-collapse model predictions, demonstrating that other formation mechanisms may be at work. We estimate that ejection from planetary systems might have a contribution comparable to that of core collapse in the formation of FFPs. Therefore, ejections due to dynamical instabilities in giant exoplanet systems must be frequent within the first 10Myr of a system's life.
We present the results of an intermediate resolution spectroscopic survey for pre-main sequence (PMS) stars in the Upper Scorpius OB association. In a 160 square-degree area we were able to identify 39 new PMS stars by follow up observations of X-ray selected stars with the multi object spectrograph FLAIR at the UK Schmidt Telescope. We also investigated the completeness of our X-ray selected sample by observing more than 100 stars that were not detected as X-ray sources, but have proper motions indicating membership to Upper Sco. While the new X-ray selected PMS stars with known proper motions have kinematics consistent with membership, none of the X-ray quiet proper motion candidates is a PMS star. We conclude that our X-ray selected sample of PMS stars seems to be rather complete. For stars in the magnitude interval 11.5<~B<~13.5 we derive a conservative lower limit of 75% completeness.
We investigate the stellar population and star formation history of the Upper Scorpius OB association, the most nearby region of recent massive star formation, over the full stellar mass range from 0.1 to 20M_{sun}_. The first part of this paper describes an extension of our large spectroscopic survey (Preibisch et al., published in 2001, Cat. <J/AJ/121/1040>) for low-mass pre-main-sequence (PMS) stars in Upper Scorpius. Using the multiobject spectrograph 2dF at the Anglo-Australian Telescope, we obtained spectra of 469 stars with magnitudes R=12.5-18.0 in a 6{deg}^2^ area, on he nights of 2001 May 16-17. Among these, we find 68 new PMS stars, nearly all of them M-type stars, by their strong lithium absorption lines. The total area covered by our 2dF survey is now 9 deg2 and contains 166 new PMS stars. Combining these results with our earlier investigation (Preibisch & Zinnecker, 1999AJ....117.2381P) yields a sample of 250 PMS stars in the mass range ~0.2 to ~2M_{sun}_.
We have refined the census of stars and brown dwarfs in the Upper Sco association (~10Myr, ~145pc) by (1) updating the selection of candidate members from our previous survey to include the high-precision astrometry from the second data release of Gaia, (2) obtaining spectra of a few hundred candidate members to measure their spectral types and verify their youth, and (3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward Upper Sco that show evidence of youth in this work and previous studies. We arrive at a catalog of 1761 objects that are adopted as members of Upper Sco. The distribution of spectral types among the adopted members is similar to those in other nearby star-forming regions, indicating a similar initial mass function. In previous studies, we have compiled mid-infrared photometry from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope for members of Upper Sco and used those data to identify the stars that show evidence of circumstellar disks; we present the same analysis for our new catalog of members. As in earlier work, we find that the fraction of members with disks increases with lower stellar masses, ranging from <~10% for >1M{sun} to ~22% for 0.01-0.3M{sun}. Finally, we have estimated the relative ages of Upper Sco and other young associations using their sequences of low-mass stars in M_G_RP__ versus G_BP_-G_RP_. This comparison indicates that Upper Sco is a factor of two younger than the {beta}Pic association (21-24Myr) according to both nonmagnetic and magnetic evolutionary models.
The Uppsala General Catalogue of Galaxies (UGC) is an essentially complete catalogue of galaxies to a limiting diameter of 1.0' and/or to a limiting apparent magnitude of 14.5 on the blue prints of the Palomar Observatory Sky Survey (POSS). Coverage is limited to the sky north of declination -02.5degrees. Galaxies smaller than 1.0' in diameter but brighter than 14.5 mag may be included from the Catalogue of Galaxies and of Clusters of Galaxies (CGCG, Zwicky et al. 1961-1968); all such galaxies in the CGCG are included in the UGC. The galaxies are ordered by 1950 right ascension. The catalogue contains descriptions of the galaxies and their surrounding areas, plus conventional system classifications and position angles for flattened galaxies. Galaxy diameters on both the blue and red POSS prints are included and the classifications and descriptions are given in such a way as to provide as accurate an account as possible of the appearance of the galaxies on the prints. Only the data portion of the published UGC is included in the machine-readable version. The order of the records is strictly by UGC number; i.e., the Addenda records follow their main catalogue counterparts in the file. The colons (indicating uncertainty) and various other codes (parentheses, brackets) are not included in the machine-readable version of the catalogue. Several possible improvements to the catalogue might consist of adding codes corresponding to the published version, a second file containing abbreviations and terminology and a third file with the extensive notes. It would also be important to add an asterisk or some other code to data records having a note in the proposed third file. This document describes the machine-readable version of the UGC as distributed by the Astronomical Data Centers. It is intended to enable users to read and process the data without problems or guesswork. For additional details regarding the classifications, measurement of apparent magnitudes, and data content, the source reference should be consulted. A copy of this document should accompany any machine-readable copy of the catalogue.
Elemental abundances analyses are performed for the Mercury-Manganese stars {upsilon} Her, {phi} Her, and HR 7018 consistent with previous studies of this series using spectrograms obtained with Reticon and CCD detectors. Comparisons of the first two analyses with those performed using coadded photographic plates show the general consistency of the derived elemental abundances. For {upsilon} Her and for {phi} Her, abundances were newly found for O, and for Al, V, Zn, and Ce, respectively. HR 7018 is discovered to be a single-lined spectroscopic binary. Its Sc abundance is the smallest of any class member with derived abundances and its Sr abundance the largest of any known HgMn star. A correlation analysis of the most complete abundance sets for 20 HgMn stars shows that the abundances of some elements are correlated with one another and some are functions of the stellar effective temperature.
We have used high-cadence radial velocity (RV) measurements from the Hobby-Eberly Telescope with existing velocities from the Lick, Elodie, Harlan J. Smith, and Whipple 60" telescopes combined with astrometric data from the Hubble Space Telescope Fine Guidance Sensors to refine the orbital parameters and determine the orbital inclinations and position angles of the ascending node of components {upsilon} And A c and d. With these inclinations and using M*=1.31M_{sun}_ as a primary mass, we determine the actual masses of two of the companions: {upsilon} And A c is 13.98^+2.3^_-5.3_M_Jup_, and {upsilon} And A d is 10.25^+0.7^_-3.3_M_Jup_. These measurements represent the first astrometric determination of mutual inclination between objects in an extrasolar planetary system, which we find to be 29.9+/-1{deg}. The combined RV measurements also reveal a long-period trend indicating a fourth planet in the system. We investigate the dynamic stability of this system and analyze regions of stability, which suggest a probable mass of {upsilon} And A b. Finally, our parallaxes confirm that u And B is a stellar companion of {upsilon} And A.
Astrometric positions of the five largest satellites are given for the oppositions of Uranus for the years 1989 to 1994. These positions were measured on 368 CCD frames obtained at the Cassegrain focus of a 1.6-m reflector. They are compared with the theoretically calculated positions from GUST86 (Laskar & Jacobson 1987). The observed minus calculated residuals referred to Oberon have standard deviations of the order of 0.05" for the three greatest Uranian satellites and 0.07" for Miranda. These residuals are comparable to the best available in the literature.
Astrometric positions of the five largest Uranian satellites from 750 CCD frames taken at the oppositions of 1995 through 1998 are presented. The images were obtained over 35 nights. Observed positions are compared with the calculated positions from GUST86. The standard deviations are better than 0.05" for the four largest satellites and 0.08" for Miranda.
In this paper, we publish measurements of 864 positions of the major satellites of Uranus made in 1995-1997 using CCD (1024"*1024") detectors attached to the 1.56-metre Astrometric Telescope at the Sheshan station near Shanghai. Analysis of the data as inter-satellite positions shows that the observations of Ariel, Umbriel, Titania and Mirand relative to Oberon have root-mean-square residuals of 0.03"-0.05", except for the innermost and faintest satellite Miranda, whose residuals exceeded 0.08" due to the proximity of Uranus.