Probability of simultaneous parallax detection for free-floating planet microlensing events near Galactic Centre

ABSTRACT The event rate and the efficiency of mass estimation for free-floating planet (FFP) microlensing events were determined from the simulation of the simultaneous parallax observations by Euclid, WFIRST, and LSST. The stellar population from the Besançon Galactic model toward (l, b) = (1°, −1.°75) was applied to our 3D microlensing model, and 30 000 parallax observations were simulated for each following FFP lens masses: Jupiter mass, Neptune mass, and Earth mass assuming the population of one FFP per star. The interstellar dust, unresolved stellar background, nearby star blending was modelled. A signal-to-noise limit considering a finite source effect determined the event detectability. The Euclid–WFIRST combination yielded 30.7 Jupiter-mass FFPs during two 30-d periods per year in parallax observation. The parallax event rate decreases to 3.9 FFPs for Earth-mass planets. The mass estimation from the parallax light curve allowed recovery of FFP masses to within a factor of 2 for 20–26 per cent of cases. The Euclid–LSST combination yielded 34.5 Jupiter-mass FFPs down to 0.5 Earth-mass FFPs for the same periods and the mass is recovered to within a factor of 2 in 20–40 per cent of cases. The event rate will be normalized by the unknown FFP abundance to recover the number of expected detections.

Astrometric and photometric study of the open cluster NGC 2323

We present a study of the open cluster NGC 2323 using astrometric and photometric data. In our study we used two methods that are able to separate open cluster?s stars from those that belong to the stellar background. Our results of calculations by these two methods indicate that: 1) according to the membership probability, NGC 2323 should contain 497 stars, 2) the cluster center should be at 07h 02m 48.s02 and -08? 20' 17''74,3) the limiting radius of NGC 2323 is 2.31 ? 0.04 pc, the surface number density at this radius is 98.16 stars pc ?2, 4) the magnitude function has a maximum at about mv = 14 mag, 5) the total mass of NGC 2323 is estimated dynamically by using astrometric data to be 890 M_, and statistically by using photometric data to be 900 M_, and 6) the distance and age of the cluster are found to be equal to 900 ? 100 pc, and 140 ? 20 Myr, respectively. Finally the dynamical evolution parameter ? of the cluster is about 436.2.

Optical Astrometry and the Global Positioning System

Astrometric accuracies of a few tens of milliarcseconds are expected to be attainable within five years by calibrating astrograph plates with optical observations of Global Positioning System (GPS) satellites against a stellar background. The line of sight from an observer on the Earth’s surface to a GPS satellite may be calculated with high accuracy. Motion on each day of the line of sight to the satellite and changes from day to day in the apparent path of the satellite are sufficiently slow to make it possible to reduce atmospheric errors by averaging. Advanced ground-based optical sensors, probably using charge coupled device technology, will be required for GPS optical astrometry.

Ancient Chinese Astronomical Observations Related to the Stellar Background on the Sky

Ancient Chinese astronomers had special interest to measure positions of celestial bodies. “Shishi Xingjing” including at least 115 stars was produced in the 4th century BC. By the 11th century, the measure of stellar coordinates was in full swing and 5 detailed measures were carried on in only 100 years. So several ancient stellar catalogs have been retained up to now. As an ancient reference system, many astronomical phenomena have been recorded on it. This is meaningful for modern astronomers to do some modern research.