Anchors for the Cosmic Distance Scale: the Cepheids U Sgr, CF Cas and CEab Cas

New and existing X-ray, UBVJHKsW(1-4), and spectroscopic observations were analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance given they host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids' period evolution (dP/dt) from ~140 years of observations, helped resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, distances derived for members of M25 and NGC 7790 are 630+-25 pc and 3.40+-0.15 kpc, respectively.Comment: To appear in Astronomy and Astrophysic

The Seven Sisters DANCe. I. Empirical isochrones, Luminosity and Mass Functions of the Pleiades cluster

The DANCe survey provides photometric and astrometric (position and proper motion) measurements for approximately 2 millions unique sources in a region encompassing $\approx$80deg$^{2}$ centered around the Pleiades cluster. We aim at deriving a complete census of the Pleiades, and measure the mass and luminosity function of the cluster. Using the probabilistic selection method described in Sarro+2014, we identify high probability members in the DANCe ($i\ge$14mag) and Tycho-2 ($V\lesssim$12mag) catalogues, and study the properties of the cluster over the corresponding luminosity range. We find a total of 2109 high probability members, of which 812 are new, making it the most extensive and complete census of the cluster to date. The luminosity and mass functions of the cluster are computed from the most massive members down to $\approx$0.025M$_{\odot}$. The size, sensitivity and quality of the sample result in the most precise luminosity and mass functions observed to date for a cluster. Our census supersedes previous studies of the Pleiades cluster populations, both in terms of sensitivity and accuracy.Comment: Language Edition Done. Final version to be published in A&A. Tables will be published at CDS. Meanwhile, they can be requested to H. Bouy (hbouy -at- cab . inta - csic . es

Properties of the solar neighbor WISE J072003.20-084651.2

The severe crowding towards the Galactic plane suggests that the census of nearby stars in that direction may be incomplete. Recently, Scholz reported a new M9 object at an estimated distance d~7 pc (WISE J072003.20-084651.2; hereafter WISE0720) at Galactic latitude b=2.3 degr. Our goals are to determine the physical characteristics of WISE0720, its kinematic properties, and to address the question if it is a binary object, as suggested in the discovery paper. Optical and infrared spectroscopy from the Southern African Large Telescope and Magellan, respectively, and spectral energy distribution fitting were used to determine the spectral type of WISE0720. The measured radial velocity, proper motion and parallax yielded its Galactic velocities. We also investigated if WISE0720 may show X-ray activity based on archival data. Our spectra are consistent with spectral type L0+/-1. We find no evidence for binarity, apart for a minor 2-sigma level difference in the radial velocities taken at two different epochs. The spatial velocity of WISE0720 does not connect it to any known moving group, instead it places the object with high probability in the old thin disk or in the thick disk. The spectral energy distribution fit hints at excess in the 12 and 22 micron WISE bands which may be due to a redder companion, but the same excess is visible in other late type objects, and it more likely implies a shortcoming of the models (e.g., issues with the effective wavelengths of the filters for these extremely cool objects, etc.) rather than a disk or redder companion. The optical spectrum shows some Halpha emission, indicative of stellar activity. Archival X-ray observations yield no detection.Comment: A&A, accepted; 9 pages, 6 figure

An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30

So far, roughly 40 quasars with redshifts greater than z=6 have been discovered. Each quasar contains a black hole with a mass of about one billion solar masses ($10^9 M_\odot$). The existence of such black holes when the Universe was less than 1 billion years old presents substantial challenges to theories of the formation and growth of black holes and the coevolution of black holes and galaxies. Here we report the discovery of an ultra-luminous quasar, SDSS J010013.02+280225.8, at redshift z=6.30. It has an optical and near-infrared luminosity a few times greater than those of previously known z>6 quasars. On the basis of the deep absorption trough on the blue side of the Ly $\alpha$ emission line in the spectrum, we estimate the proper size of the ionized proximity zone associated with the quasar to be 26 million light years, larger than found with other z>6.1 quasars with lower luminosities. We estimate (on the basis of a near-infrared spectrum) that the black hole has a mass of $\sim 1.2 \times 10^{10} M_\odot$, which is consistent with the $1.3 \times 10^{10} M_\odot$ derived by assuming an Eddington-limited accretion rate.Comment: 24 pages, 4 figures plus 4 extended data figures, published in Nature on 26 February 201

Uncovering the kiloparsec-scale stellar ring of NGC5128

We reveal the stellar light emerging from the kiloparsec-scale, ring-like structure of the NGC5128 (Centaurus A) galaxy in unprecedented detail. We use arcsecond-scale resolution near infrared images to create a "dust-free" view of the central region of the galaxy, which we then use to quantify the shape of the revealed structure. At the resolution of the data, the structure contains several hundreds of discreet, point-like or slightly elongated sources. Typical extinction corrected surface brightness of the structure is K_S = 16.5 mag/arcsec^2, and we estimate the total near infrared luminosity of the structure to be M = -21 mag. We use diffraction limited (FWHM resolution of ~ 0.1", or 1.6 pc) near infrared data taken with the NACO instrument on VLT to show that the structure decomposes into thousands of separate, mostly point-like sources. According to the tentative photometry, the most luminous sources have M_K = -12 mag, naming them red supergiants or relatively low-mass star clusters. We also discuss the large-scale geometry implied by the reddening signatures of dust in our near infrared images.Comment: 5 pages, 4 figures, accepted for publication in A&A Letters. A version with high resolution images can be downloaded from http://www.helsinki.fi/~jtkainul/CenALette

Automated search for star clusters in large multiband surveys: II. Discovery and investigation of open clusters in the Galactic plane

Automated search for star clusters in J,H,K_s data from 2MASS catalog has been performed using the method developed by Koposov et. al (2008). We have found and verified 153 new clusters in the interval of the galactic latitude -24 < b < 24 degrees. Color excesses E(B-V), distance moduli and ages were determined for 130 new and 14 yet-unstudied known clusters. In this paper, we publish a catalog of coordinates, diameters, and main parameters of all the clusters under study. A special web-site available at http://ocl.sai.msu.ru has been developed to facilitate dissemination and scientific usage of the results.Comment: 9 pages, 3 tables, 5 figures, accepted to Astronomy Letter

Discovery of a new Y dwarf: WISE J030449.03-270508.3

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record [D. J. Pinfield, et al, Discovery of a new Y dwarf: WISE J030449.03−270508.3, MNRAS, Vol. 444 (2): 1931-1939, September 2014] is available online at: https://doi.org/10.1093/mnras/stu1540.We present a new Y dwarf, WISE J030449.03−270508.3, confirmed from a candidate sample designed to pick out low-temperature objects from the Wide-field Infrared Survey Explorer (WISE) data base. The new object is typed Y0pec following a visual comparison with spectral standards, and lies at a likely distance of 10–17 pc. Its tangential velocity suggests thin disc membership, but it shows some spectral characteristics that suggest that it may be metal poor and/or older than previously identified Y0 dwarfs. Based on trends seen for warmer late-type T dwarfs, the Y-band flux peak morphology is indicative of sub-solar metallicity, and the enhanced red wing of the J-band flux peak offers evidence for high gravity and/or low metallicity (with associated model trends suggesting an age closer to ∼10 Gyr and mass in the range 0.02–0.03 Mȯ). This object may thus be extending the population parameter space of the known Y0 dwarfs.Peer reviewe

Realistic Equations of State for the Primeval Universe

Early universe equations of state including realistic interactions between constituents are built up. Under certain reasonable assumptions, these equations are able to generate an inflationary regime prior to the nucleosynthesis period. The resulting accelerated expansion is intense enough to solve the flatness and horizon problems. In the cases of curvature parameter \kappa equal to 0 or +1, the model is able to avoid the initial singularity and offers a natural explanation for why the universe is in expansion.Comment: 32 pages, 5 figures. Citations added in this version. Accepted EPJ

One more neighbor: The first brown dwarf in the VVV survey

Context. The discovery of brown dwarfs (BDs) in the solar neighborhood and young star clusters has helped to constraint the low-mass end of the stellar mass function and the initial mass function. We use data of the Vista Variables in the V\'ia L\'actea (VVV), a near-infrared (NIR) multiwavelength (Z Y J H Ks) multi-epoch (Ks) ESO Public Survey mapping the Milky Way bulge and southern Galactic plane to search for nearby BDs. Aims. The ultimate aim of the project is to improve the completeness of the census of nearby stellar and substellar objects towards the Galactic bulge and inner disk regions. Methods. Taking advantage of the homogeneous sample of VVV multi-epoch data, we identified stars with high proper motion (> 0.1"/yr), and then selected low-mass objects using NIR colors. We searched for a possible parallax signature using the all available Ks band epochs. We set some constraints on the month-to-year scale Ks band variability of our candidates, and even searched for possible transiting companions. We obtained NIR spectra to properly classify spectral type and then the physical properties of the final list of candidates. Results. We report the discovery of VVV BD001, a new member of the local volume-limited sample (within 20pc from the sun) with well defined proper motion, distance, and luminosity. The spectral type of this new object is an L5+-1, unusually blue dwarf. The proper motion for this BD is PM(\alpha)=-0.5455+-0.004 "/yr, PM(\delta)=-0.3255+-0.004 "/yr, and it has a parallax of 57+-4 mas which translates into a distance of 17.5 +- 1.1 pc. VVV BD001 shows no evidence of variability (\Delta Ks <0.05mag) over two years, especially constrained on a six month scale during the year 2012.Comment: 5 pages, 4 figures, 1 table, Accepted for publication in Astronomy and Astrophysics Letter

Model-Independent Diagnostics of Highly Reddened Milky Way Star Clusters: Age Calibration

The next generation near- and mid-infrared Galactic surveys will yield a large number of new highly obscured star clusters. Detailed characterization of these new objects with spectroscopy is time-consuming. Diagnostic tools that will be able to characterize clusters based only on the available photometry will be needed to study large samples of the newly found objects. The brightness difference between the red clump and the main-sequence turn-off point have been used as a model-independent age calibrator for clusters with ages from a few 10$^8$ to 10$^{10}$ yr in the optical. Here we apply for the first time the method in the near-infrared. We calibrated this difference in $K$-band, which is likely to be available for obscured clusters, and we apply it to a number of test clusters with photometry comparable to the one that will be yielded by the current or near-future surveys. The new calibration yields reliable ages over the range of ages for which the red clump is present in clusters. The slope of the relation is smoother than that of the corresponding $V$-band relation, reducing the uncertainty in the age determinations with respect to the optical ones.Comment: 5 pages, 5 eps figure, accepted for publication in Astronomy and Astrophysic