338 research outputs found
Clustering of Local Group Distances: Publication Bias or Correlated Measurements? VII. A Distance Framework out to 100 Mpc
No full textClustering of local group distances: publication bias or correlated measurements? VI. Extending to Virgo cluster dstances
No full textClustering of Local Group Distances: Publication Bias or Correlated Measurements? V. Galactic Rotation Constants
No full textAs part of an extensive data mining effort, we have compiled a database of 162 Galactic rotation speed measurements at R-0 (the solar Galactocentric distance), circle minus(0). Published between 1927 and 2017 June, this represents the most comprehensive set of circle minus(0) values since the 1985 meta-analysis that led to the last revision of the International Astronomical Union's recommended Galactic rotation constants. Although we do not find any compelling evidence for the presence of "publication bias" in recent decades, we find clear differences among the circle minus(0) values and the circle minus(0)/R-0 ratios resulting from the use of different tracer populations. Specifically, young tracers (including OB and supergiant stars, masers, Cepheid variables, H II regions, and young open clusters), as well as kinematic measurements of Sgr A* near the Galactic Center, imply a significantly larger Galactic rotation speed at the solar circle and a higher circle minus(0)/R-0 ratio (i.e., circle minus(0) = 247 +/- 3 km s(-1) and circle minus(0)/R-0 = 29.81 +/- 0.32 km s(-1) kpc(-1); statistical uncertainties only) than any of the tracers dominating the Galaxy's mass budget (i.e., field stars and the HI/CO distributions). Using the latter to be most representative of the bulk of the Galaxy's matter distribution, we arrive at an updated set of Galactic rotation constants, circle minus(0) = 225 +/- 3 statistical +/- 10 systematic km s-(1), R-0 = 8.3 +/- 0.2 statistical +/- 0.4 systematic kpc, and circle minus(0)/R-0 = 27.12 +/- 0.39 statistical 1.78 systematic km s(-1) kpc(-1).National Natural Science Foundation of China [11373010, 11633005, U1631102]; PRIN-MIUR [2010LY5N2T]SCI(E)ARTICLE223
Variability in the Milky Way: Contact Binaries as Diagnostic Tools
No full textWe used the 50 cm Binocular Network (50BiN) telescope at Delingha Station (Qinghai Province) of Purple Mountain Observatory (Chinese Academy of Sciences) to obtain simultaneous V- and R-band observations of the old open cluster NGC 188. Our aim was a search for populations of variable stars. We derived light-curve solutions for six W Ursae Majoris (W UMa) eclipsing-binary systems and estimated their orbital parameters. The resulting distance to the W UMas is independent of the physical characteristics of the host cluster. We next determined the current best period luminosity relations for contact binaries (CBs; scatter sigma < 0.10 mag). We conclude that CBs can be used as distance tracers with better than 5% uncertainty. We apply our new relations to the 102 CBs in the Large Magellanic Cloud, which yields a distance modulus of (m - M)v,0 = 18.41 +/- 0.20 mag.CPCI-S(ISTP)23-2751
CLUSTERING OF LOCAL GROUP DISTANCES: PUBLICATION BIAS OR CORRELATED MEASUREMENTS? IV. THE GALACTIC CENTER
No full textAiming at deriving a statistically well-justified Galactic Center distance, R-0, and reducing any occurrence of publication bias, we compiled the most comprehensive and most complete database of Galactic Center distances available to date, containing 273 new or revised R-0 estimates published since records began in 1918 October until 2016 June. We separate our R-0 compilation into direct and indirect distance measurements. The latter include a large body of estimates that rely on centroid determinations for a range of tracer populations, as well as measurements based on kinematic observations of objects at the solar circle, combined with a mass and/or rotational model of the Milky Way. Careful assessment of the Galactic Center distances resulting from orbital modeling and statistical parallax measurements in the Galactic nucleus yields our final Galactic Center distance recommendation of R-0 = 8.3 +/- 0.2(statistical) +/- 0.4(systematic) kpc. The centroid-based distances are in good agreement with this recommendation. Neither the direct measurements nor the post-1990 centroid-based distance determinations suggest that publication bias may be important. The kinematics-based distance estimates are affected by significantly larger uncertainties, but they can be used to constrain the Galaxy's rotation velocity at the solar galactocentric distance, Theta(0). Our results imply that the International-Astronomical-Union-recommended Galactic Center distance (R-0(IAU) = 8.5 kpc) needs a downward adjustment, while its Theta(0) recommendation (Theta(0) = 220 km s(-1)) requires a substantial upward revision.National Natural Science Foundation of China [11373010, 11633005, U1631102]; PRIN-MIUR [2010LY5N2T]SCI(E)ARTICLE122
Ten Simple Rules for Establishing International Research Collaborations.
No full textSuccessful modern research collaborations increasingly include scientists based in different countries. This is partially driven by the need to engage with interdisciplinary science, access innovative approaches to problem solving, and acquire expertise beyond that which your own research group covers. It is also a great way to establish a worldwide network of colleagues with a variety of backgrounds-scientific, cultural, or otherwise. While international collaborations can be very rewarding, both professionally and from a personal perspective, they come with distinct difficulties and pitfalls that one should be aware of a priori. Nevertheless, cultivating an acute awareness of these issues will likely offer rich returns to internationally minded scientists, given that international research collaborations continue to expand, and many are now being established beyond the traditional power players, the North American and European research communities [1].SCI(E)PubMedEDITORIAL [email protected]
Mercer 5: A probable new globular cluster in the Galactic bulge
No full textWe present a detailed study of a dust-obscured Galactic star cluster Mercer 5 ([MCM2005b] 5) in an extremely crowded field in the Milky Way. Near-infrared (near-IR) photometry from United Kingdom Infrared Digital Sky Surveys (UKIDSS) and the Son of ISAAC on the New Technology Telescope (SofI/NTT), combined with near-IR spectroscopy also from SofI, indicates that it is almost certainly a Galactic globular cluster, located at the edge of the Galactic bulge. The cluster suffers ~9 mag of visual extinction, with strong evidence for an extinction gradient across the cluster. A simulation of the differential reddening in the cluster using empirical data from NGC 6539 (chosen because it had high signal-to-noise ratio data and low field star contamination) as a template mimics the observations extremely well. This simulation and other arguments are used to indicate that the most prominent clump of stars in the colour-magnitude diagrams is a horizontal branch clump. On this basis we conclude that the cluster is at a distance of ~5.5kpc and suffers from visual extinction ranging from ~8.5 to ~12.5 mag. Alternative explanations for its nature, such as a young cluster or an old open cluster, are much less likely, on the grounds of no visible main sequence or stars with IR excesses for the former and location versus lifetime arguments for the latter. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
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