Day 1381

Wednesday.

1803.04470
Conservative cosmology: combining data with allowance for unknown systematics
Bernal, Peacock

When combining data sets to perform parameter inference, the results will be unreliable if there are unknown systematics in data or models.  Here, introduce a flexible methodology, BACCUS: BAyesian Conservative Constraints and Unknown Systematics, which deals in a conservative way with the problem of data combination, for any degree of tension between experiments.  Introduce hyper parameters that describe a bias in each model parameter for each class of experiments.  A conservative posterior for the model parameters is then obtained by marginalization both over these unknown shifts and over the width of their prior.  Contrast this approach with an existing hyper parameter method in which each individual likelihood is scaled, comparing the performance of each approach and their combination in application to some idealized models.  Using only these rescaling hyper parameters is not a suitable approach for the current observational situation, in which internal null tests of the errors are passed, and yet different experiments prefer models that are in poor agreement.  The possible existence of large shift systematics cannot be constrained with a smaller number of data sets, leading to extended tails on the conservative posterior distributions.  Illustrate the method with the case of the H0 tension between results from the cosmic distance ladder and physical measurements that rely on the standard cosmological model.


1803.04642
The value of astrometry for exoplanet science
Bendek, et al

Exoplanets mass measurements will be a critical next step to assess the habitability of Earth-like planets a key aspect of the 2020 vision in the previous decadal survey and also central to NASA's strategic priorities.  Precision astrometry delivers measurement of exoplanet masses, allowing discrimination of rocky planets from water worlds and enabling much better modeling of their atmosphere improving species retrieval from spectroscopy.  The scientific potential of astrometry will be enormous.  The intrinsic astrophysical noise floor set by star spots and stellar surface activity is about a factor of 10 more benign for astrometry than for the more established technique of Radial Velocity, widening the discovery region and pushing detection thresholds to lower masses than previously possible.  On the instrumental side, precision astrometry is limited by optical field distortion and detector calibration issues.  Both technical challenges are now being addressed successfully in the laboratory.  However, identified the need to continue these technology development efforts to achieve sub-microarcsecond astrometry precision necessary for detection and characterization of Earth-like planets around nearby FGK stars.  The international community has realized the importance of astrometry, and various astrometry missions have been proposed and under development, with a few high profile missions now operational.  Believe that it is vital for the U.S. scientific community to participate in the development of these new technologies and scientific discoveries.  Recommend exploring alternatives to incorporate astrometric capabilities into future exoplanet flagship missions such as HABEX and LUVOIR, substantially increasing the scientific return associated with the expected yield of earth-like planets to be recovered.


1803.04869
Rapidly evolving transients in the Dark Energy Survey
Pursiainen, Childress, et al

Present the results of a search for rapidly evolving transients in the DES SN Programme. These events are characterized by fast light curve evolution (rise to peak in <~10d and exponential decline in <~30d after peak).  Discovered 72 events, including 37 transients with a spectroscopic redshift from host galaxy spectral features.  The 37 events increase the total number of rapid optical transients by more than factor of 2.  They are found at a wide range of redshifts (0.05<z<1.56) and peak brightnesses (-15.75>M_g>-22.25).  The multi band photometry is well fit by a blackbody up to few weeks after peak.  The events appear to be hot (T~10000-30000K) and large (R~1e14-2e15 cm) at peak, and generally expand and cool in time, though some events show evidence for a receding photosphere with roughly constant temperature.  Spectra taken around peak are dominated by a blue featureless continuum consistent with hot, optical thick ejecta.  Compare the events with a previously suggested physical scenario involving shock breakout in an optically thick wind surrounding a core-collapse supernova (CCSNe), conclude that current models for such a scenario might need an additional power source to describe the exponential decline.  Find these transients tend to favor star-forming host galaxies, which could be consistent with a core-collapse origin.  However, more detailed modeling of the light curves is necessary to determine their physical origin.