C. S. Botzler

Unbound or distant planetary mass population detected by gravitational microlensing

Since 1995, more than 500 exoplanets have been detected using different techniques, of which 12 were detected with gravitational microlensing. Most of these are gravitationally bound to their host stars. There is some evidence of free-floating planetary-mass objects in young star-forming regions, but these objects are limited to massive objects of 3 to 15 Jupiter masses with large uncertainties in photometric mass estimates and their abundance. Here, we report the discovery of a population of unbound or distant Jupiter-mass objects, which are almost twice () as common as main-sequence stars, based on two years of gravitational microlensing survey observations towards the Galactic Bulge. These planetary-mass objects have no host stars that can be detected within about ten astronomical units by gravitational microlensing. However, a comparison with constraints from direct imaging suggests that most of these planetary-mass objects are not bound to any host star. An abrupt change in the mass function at about one Jupiter mass favours the idea that their formation process is different from that of stars and brown dwarfs. They may have formed in proto-planetary disks and subsequently scattered into unbound or very distant orbits.

Masses and Orbital Constraints for the OGLE-2006-BLG-109Lb,c Jupiter/Saturn Analog Planetary System

We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of , Mb = 231 ± 19 M ⊕, and Mc = 86 ± 7 M ⊕. The Saturn-analog planet in this system had a planetary light-curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of and an orbital inclination of . The 95% confidence level lower limit on the inclination of i > 49° implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of 30 m aperture.

MOA-2011-BLG-293Lb: A TEST OF PURE SURVEY MICROLENSING PLANET DETECTIONS

Mathematical and Physical Sciences: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)

The Munich near-infrared cluster survey - I.:field selection, object extraction and photometry

The Munich Near-Infrared Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K′ band. It covers an area of roughly 1 deg2 in the K′ and J near-IR passbands. The survey area consists of 16 6×6 arcmin2 fields targeted at QSOs with redshifts 0.5<z<2 and seven 28×13 arcmin2 strips targeted at ‘random’ high Galactic latitude fields. 10 of the QSO fields were additionally imaged in R and I, and 0.6 deg2 of the randomly selected fields were also imaged in the V, R and I bands. The resulting object catalogues were strictly selected in K′, having a limiting magnitude (50 per cent completeness) of K′∼19.5 mag and J∼21 mag, sufficiently deep to detect passively evolving systems up to a redshift of z≲1.5 and luminosity of 0.5L*. The optical data reach a depth of roughly R∼23.5 mag. The main scientific aims of the project are the identification of galaxy clusters at redshifts around unity and the selection of a large sample of field early-type galaxies at 0<z<1.5 for evolutionary studies. In this paper – the first in a series – we describe the concept of the survey, the selection of the survey fields, the near-IR and optical imaging and data reduction, object extraction, and the construction of photometric catalogues. Finally, we show the J−K′ versus K′ colour–magnitude diagram and the R−J versus J−K′, V−I versus J−K′, and V−I versus V−R colour–colour diagrams for MUNICS objects, together with stellar population synthesis models for different star formation histories, and conclude that the data set presented is suitable for extracting a catalogue of massive field galaxies in the redshift range 0.5≲z≲1.5 for evolutionary studies and follow-up observations.

The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf

Parallax is the most fundamental technique for measuring distances to astronomical objects. Although terrestrial parallax was pioneered over 2000 years ago by Hipparchus (ca. 140 B.C.E.) to measure the distance to the Moon, the baseline of the Earth is so small that terrestrial parallax can generally only be applied to objects in the Solar System. However, there exists a class of extreme gravitational microlensing events in which the effects of terrestrial parallax can be readily detected and so permit the measurement of the distance, mass, and transverse velocity of the lens. Here we report observations of the first such extreme microlensing event OGLE-2007-BLG-224, from which we infer that the lens is a brown dwarf of mass M = 0.056 ± 0.004 M ☉, with a distance of 525 ± 40 pc and a transverse velocity of 113 ± 21 km s–1. The velocity places the lens in the thick disk, making this the lowest-mass thick-disk brown dwarf detected so far. Follow-up observations may allow one to observe the light from the brown dwarf itself, thus serving as an important constraint for evolutionary models of these objects and potentially opening a new window on substellar objects. The low a priori probability of detecting a thick-disk brown dwarf in this event, when combined with additional evidence from other observations, suggests that old substellar objects may be more common than previously assumed.

A terrestrial planet in a ~1-AU orbit around one member of a ∼15-AU binary

Impolite planet ignores hosts partner Many known exoplanets (planets outside our own solar system) are hosted by binary systems that contain two stars. These planets normally circle around both of their stars. Using microlensing data taken with a worldwide network of telescopes, Gould et al. found a planet twice the mass of Earth that circles just one of a pair of stars. The same approach has the potential to uncover other similar star systems and help to illuminate some of the mysteries of planet formation. Science, this issue p. 46 Microlensing observations reveal an exoplanet twice the mass of Earth circling just one member of a binary system. Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earth’s) and lies projected at ~0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planet’s temperature is much lower, <60 Kelvin, because the host star is only 0.10 to 0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host itself orbits a slightly more massive companion with projected separation of 10 to 15 AU. This detection is consistent with such systems being very common. Straightforward modification of current microlensing search strategies could increase sensitivity to planets in binary systems. With more detections, such binary-star planetary systems could constrain models of planet formation and evolution.

Finding structures in photometric redshift galaxy surveys: an extended friends‐of‐friends algorithm

We present a modified version of the friends-of-friends (FOF) structure-finding algorithm, designed specifically to locate groups or clusters of galaxies in photometric redshift data sets. The main objective of this paper is to show that this extended friends-of-friends (hereafter EXT-FOF) algorithm yields results almost identical to the original FOF, if applied to a spectroscopic redshift data set, and a rather conservative catalogue of structures, in case of a data set with simulated photometric redshifts. Therefore, we create group catalogues for the first Center for Astrophysics Redshift Survey (CFA1), as well as for the Las Campanas Redshift Survey (LCRS), both of which being spectroscopic surveys, using FOF algorithms. We then apply our new algorithm to said surveys and compare the resulting structure catalogue. Furthermore, we bestow simulated photometric redshifts on the LCRS galaxies, and use the EXT-FOF to detect structures, which we compare in size and composition to the ones found in the original, spectroscopic data set. We will show that the properties of this modified algorithm are well understood and that it is suited for finding structures in photometric data sets. This is the first paper in a series of papers, dealing with the application of our new cluster finding algorithm to various photometric redshift galaxy surveys.

OGLE-2013-BLG-0102LA,B: MICROLENSING BINARY WITH COMPONENTS AT STAR/BROWN DWARF AND BROWN DWARF/PLANET BOUNDARIES

We present the analysis of the gravitational microlensing event OGLE-2013-BLG-0102. The light curve of the event is characterized by a strong short-term anomaly superposed on a smoothly varying lensing curve with a moderate magnification

OGLE-2005-BLG-153: Microlensing Discovery and Characterization of a Very Low Mass Binary

A_{\rm max}\sim 1.5

The Munich Near-Infrared Cluster Survey – IV. Biases in the completeness of near-infrared imaging data

. It is found that the event was produced by a binary lens with a mass ratio between the components of