Abstract
The Nancy Grace Roman Space Telescope (Roman) will perform a Galactic Exoplanet Survey (RGES) to discover bound exoplanets with semimajor axes greater than 1 au using gravitational ...microlensing. Roman will even be sensitive to planetary-mass objects that are not gravitationally bound to any host star. Such free-floating planetary-mass objects (FFPs) will be detected as isolated microlensing events with timescales shorter than a few days. A measurement of the abundance and mass function of FFPs is a powerful diagnostic of the formation and evolution of planetary systems, as well as the physics of the formation of isolated objects via direct collapse. We show that Roman will be sensitive to FFP lenses that have masses from that of Mars (0.1
M
⊕
) to gas giants (
M
≳ 100
M
⊕
) as isolated lensing events with timescales from a few hours to several tens of days, respectively. We investigate the impact of the detection criteria on the survey, especially in the presence of finite-source effects for low-mass lenses. The number of detections will depend on the abundance of such FFPs as a function of mass, which is at present poorly constrained. Assuming that FFPs follow the fiducial mass function of cold, bound planets adapted from Cassan et al., we estimate that Roman will detect ∼250 FFPs with masses down to that of Mars (including ∼60 with masses ≤
M
⊕
). We also predict that Roman will improve the upper limits on FFP populations by at least an order of magnitude compared to currently existing constraints.
Abstract
For microlenses with sufficiently low mass, the angular radius of the source star can be much larger than the angular Einstein ring radius of the lens. For such extreme finite source effect ...(EFSE) events, finite source effects dominate throughout the duration of the event. Here, we demonstrate and explore a continuous degeneracy between multiple parameters of such EFSE events. The first component in the degeneracy arises from the fact that the directly observable peak change of the flux depends on both the ratio of the angular source radius to the angular Einstein ring radius and the fraction of the baseline flux that is attributable to the lensed source star. The second component arises because the directly observable duration of the event depends on both the impact parameter of the event and the relative lens-source proper motion. These two pairwise degeneracies become coupled when the detailed morphology of the light curve is considered, especially when including a limb-darkening profile of the source star. We derive these degeneracies mathematically through analytic approximations and investigate them further numerically with no approximations. We explore the likely physical situations in which these mathematical degeneracies may be realized and potentially broken. As more and more low-mass lensing events (with ever decreasing Einstein ring radii) are detected with improving precision and increasing cadence from microlensing surveys, one can expect that more of these EFSE events will be discovered. In particular, the detection of EFSE microlensing events could increase dramatically with the Roman Space Telescope Galactic Bulge Time Domain Survey.
Abstract
The Nancy Grace Roman Space Telescope (Roman) will provide an enormous number of microlensing light curves with much better photometric precision than ongoing ground-based observations. Such ...light curves will enable us to observe high-order microlensing effects which have been previously difficult to detect. In this paper, we investigate Roman's potential to detect and characterize short-period planets and brown dwarfs (BDs) in source systems using the orbital motion of source stars, the so-called xallarap effect. We analytically estimate the measurement uncertainties of xallarap parameters using Fisher matrix analysis. We show that the Roman Galactic Exoplanet Survey can detect warm Jupiters with masses down to 0.5
M
Jup
and orbital periods of 30 days via the xallarap effect. Assuming a planetary frequency function from Cumming et al., we find Roman will detect ∼10 hot and warm Jupiters and ∼30 close-in BDs around microlensed source stars during the microlensing survey. These detections are likely to be accompanied by the measurements of the companion’s masses and orbital elements, which will aid in the study of the physical properties for close-in planet and BD populations in the Galactic bulge.
Abstract
Little is observationally known about the progenitors of Type Ibc supernovae (SNe) or the typical activity of SNe progenitors in their final years. Here, we analyse deep Large Binocular ...Telescope imaging data spanning the 4 yr before and after the Type Ibc SN 2012fh using difference imaging. We place 1σ upper limits on the detection of the progenitor star at M
U
> −3.8, M
B
> −3.1, M
V
> −3.8 and M
R
> −4.0 mag. These limits are the tightest placed on a Type Ibc SN to date and they largely rule out single star evolutionary models in favour of a binary channel as the origin of this SN. We also constrain the activity of the progenitor to be small on an absolute scale, with the RMS UBVR optical variability ≲ 2500 L⊙ and long-term dimming or brightening trends ≲ 1000 L⊙ yr−1 in all four bands.
We present a computationally tractable implementation of spectro-perfectionism, a method which minimizes error imparted by spectral extraction. We develop our method in conjunction with a full raw ...reduction pipeline for the MINiature Exoplanet Radial Velocity Array (MINERVA), capable of performing both optimal extraction and spectro-perfectionism. Although spectro-perfectionism remains computationally expensive, our implementation can extract a MINERVA exposure in approximately 30 minutes. We describe our localized extraction procedure and our approach to point-spread function (PSF) fitting. We compare the performance of both extraction methods on a set of 119 exposures on HD 122064, an RV standard star. Both the optimal extraction and spectro-perfectionism pipelines achieve nearly identical RV precision under a six-exposure chronological binning. We discuss the importance of reliable calibration data for PSF fitting and the potential of spectro-perfectionism for future precise radial velocity exoplanet studies.
We present the discovery of two extended ∼0.12 mag dimming events of the weak-lined T Tauri star V1334. The start of the first event was missed but came to an end in late 2003, and the second began ...in 2009 February, and continues as of 2016 November. Since the egress of the current event has not yet been observed, it suggests a period of >13 years if this event is periodic. Spectroscopic observations suggest the presence of a small inner disk, although the spectral energy distribution shows no infrared excess. We explore the possibility that the dimming events are caused by an orbiting body (e.g., a disk warp or dust trap), enhanced disk winds, hydrodynamical fluctuations of the inner disk, or a significant increase in the magnetic field flux at the surface of the star. We also find a ∼0.32 day periodic photometric signal that persists throughout the 2009 dimming which appears to not be due to ellipsoidal variations from a close stellar companion. High-precision photometric observations of V1334 Tau during K2 campaign 13, combined with simultaneous photometric and spectroscopic observations from the ground, will provide crucial information about the photometric variability and its origin.
The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated observatory of four 0.7 m robotic telescopes fiber-fed to a KiwiSpec spectrograph. The MINERVA mission is to discover ...super-Earths in the habitable zones of nearby stars. This can be accomplished with MINERVA's unique combination of high precision and high cadence over long time periods. In this work, we detail changes to the MINERVA facility that have occurred since our previous paper. We then describe MINERVA's robotic control software, the process by which we perform 1D spectral extraction, and our forward modeling Doppler pipeline. In the process of improving our forward modeling procedure, we found that our spectrograph's intrinsic instrumental profile is stable for at least nine months. Because of that, we characterized our instrumental profile with a time-independent, cubic spline function based on the profile in the cross dispersion direction, with which we achieved a radial velocity precision similar to using a conventional "sum-of-Gaussians" instrumental profile: 1.8 m s−1 over 1.5 months on the RV standard star HD 122064. Therefore, we conclude that the instrumental profile need not be perfectly accurate as long as it is stable. In addition, we observed 51 Peg and our results are consistent with the literature, confirming our spectrograph and Doppler pipeline are producing accurate and precise radial velocities.
The Radial Velocity of OGLE-2015-BLG-0966S Johnson, Samson A.; Yee, Jennifer C.
Publications of the Astronomical Society of the Pacific,
07/2017, Letnik:
129, Številka:
977
Journal Article
Recenzirano
Odprti dostop
The distance to the planetary system OGLE-2015-BLG-0966L and the separation between the planet and its host star are ambiguous due to an ambiguity in the distance to the source star. We attempt to ...break this degeneracy by measuring the systemic radial velocity of the source star measured from a spectrum taken while the source was highly magnified. Our measurement of v LSR = 54.2 0.3 km s − 1 does not definitively resolve the nature of the source, but supports the general conclusion that the source is in the bulge. This work demonstrates that even a low signal-to-noise spectrum has the potential to provide useful information for characterizing microlensing source stars.
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