skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Global optimization-based reference star differential imaging for high-contrast exoplanet imaging survey
ABSTRACT We propose a data reduction approach called global optimization-based reference star differential imaging (G-RDI), which can be used for exoplanet imaging survey, where large numbers of target stars from the same young stellar association are imaged and where no field rotation is needed. One of the unique features of our G-RDI is that we select reference stars from other scientific target stars in the same stellar association to optimize for high-contrast imaging with a target star, which maximizes the observational efficiency and also delivers good performance to remove the speckle noise so that high contrast is achievable even at a small inner working angle (IWA) to the host star of being imaged. We proposed the G-RDI that is optimized for high-contrast exoplanet imaging at a small IWA and to provide a contrast that is significantly better than the current reference star differential imaging (RDI) method. In addition, we also propose the use of multiple reference stars and found that our G-RDI can further deliver better performance in that case. The result was compared with other exoplanet data reduction techniques, including the traditional RDI, and it indicated that our G-RDI with two reference stars can significantly improve the contrast performance at a small IWA with a high observational efficiency – two critical features that current data reduction techniques cannot offer. This approach could be used with both equatorial and alt-azimuth mount telescopes, and provides a new option for future exoplanet imaging surveys with high observational efficiency at a small IWA.  more » « less
Award ID(s):
1906166 1607921
PAR ID:
10274340
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
502
Issue:
2
ISSN:
0035-8711
Page Range / eLocation ID:
2158 to 2171
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; (, The Astronomical Journal)
    Abstract We present Super-RDI, a unique framework for the application of reference star differential imaging (RDI) to Keck/NIRC2 high-contrast imaging observations with the vortex coronagraph. Super-RDI combines frame selection and signal-to-noise ratio (S/N) optimization techniques with a large multiyear reference point-spread function (PSF) library to achieve optimal PSF subtraction at small angular separations. We compile an ∼7000 frame reference PSF library based on a set of 288 new Keck/NIRC2 L ′ sequences of 237 unique targets acquired between 2015 and 2019 as part of two planet-search programs designed for RDI, one focusing on nearby young M dwarfs and the other targeting members of the Taurus star-forming region. For our data set, synthetic companion injection-recovery tests reveal that frame selection with the mean-squared error metric combined with Karhunen–Loève Image-Processing-based PSF subtraction using 1000–3000 frames and ≲500 principal components yields the highest average S/N for injected synthetic companions. We uniformly reduce targets in the young M-star survey with both Super-RDI and angular differential imaging (ADI). For the typical parallactic angle rotation of our data set (∼10°), Super-RDI performs better than a widely used implementation of ADI-based PSF subtraction at separations ≲0.″4 (≈5λ/D), gaining an average of 0.25 mag in contrast at 0.″25 and 0.4 mag in contrast at 0.″15. This represents a performance improvement in separation space over RDI with single-night reference star observations (∼100 frame PSF libraries) applied to a similar Keck/NIRC2 data set in previous work. We recover two known brown dwarf companions and provide detection limits for 155 targets in the young M-star survey. Our results demonstrate that increasing the PSF library size with careful selection of reference frames can improve the performance of RDI with the Keck/NIRC2 vortex coronagraph in L ′ . 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, The Astronomical Journal)
    Abstract We present the validation of a transiting low-density exoplanet orbiting the M2.5 dwarf TOI 620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We utilize photometric data from both TESS and ground-based follow-up observations to validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios. High-contrast imaging data are used to resolve the stellar host and exclude stellar companions at separations ≳0.″2. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with multiple precision radial velocity (PRV) spectrographs to confirm the planetary nature of the transiting exoplanet. We calculate a 5σupper limit ofMP< 7.1M⊕andρP< 0.74 g cm−3, and we identify a nontransiting 17.7 day candidate. We also find evidence for a substellar (1–20MJ) companion with a projected separation ≲20 au from a combined analysis of Gaia, adaptive optics imaging, and RVs. With the discovery of this outer companion, we carry out a detailed exploration of the possibilities that TOI 620 b might instead be a circum-secondary planet or a pair of eclipsing binary stars orbiting the host in a hierarchical triple system. We find, under scrutiny, that we can exclude both of these scenarios from the multiwavelength transit photometry, thus validating TOI 620 b as a low-density exoplanet transiting the central star in this system. The low density of TOI 620 b makes it one of the most amenable exoplanets for atmospheric characterization, such as with the James Webb Space Telescope and Ariel, validated or confirmed by the TESS mission to date. 
    more » « less
  3. (, Publications of the Astronomical Society of the Pacific)
    Abstract This tutorial is an introduction to High-Contrast Imaging, a technique that enables astronomers to isolate light from faint planets and/or circumstellar disks that would otherwise be lost amidst the light of their host stars. Although technically challenging, high-contrast imaging allows fordirectcharacterization of the properties of circumstellar sources. The intent of the article is to provide newcomers to the field a general overview of the terminology, observational considerations, data reduction strategies, and analysis techniques high-contrast imagers employ to identify, vet, and characterize planet and disk candidates. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal)
    Abstract Stellar magnetic fields have a major impact on space weather around exoplanets orbiting low-mass stars. From an analysis of Zeeman-broadened Feilines measured in near-infrared SDSS/APOGEE spectra, mean magnetic fields are determined for a sample of 29 M dwarf stars that host closely orbiting small exoplanets. The calculations employed the radiative transfer code Synmast and MARCS stellar model atmospheres. The sample M dwarfs are found to have measurable mean magnetic fields ranging between ∼0.2 and ∼1.5 kG, falling in the unsaturated regime on the 〈B〉 versusProtplane. The sample systems contain 43 exoplanets, which include 23 from Kepler, nine from K2, and nine from Transiting Exoplanet Survey Satellite. We evaluated their equilibrium temperatures, insolation, and stellar habitable zones and found that only Kepler-186f and TOI-700d are inside the habitable zones of their stars. Using the derived values of 〈B〉 for the stars Kepler-186 and TOI-700 we evaluated the minimum planetary magnetic field that would be necessary to shield the exoplanets Kepler-186f and TOI-700d from their host star’s winds, considering reference magnetospheres with sizes equal to those of the present-day and young Earth, respectively. Assuming a ratio of 5% between large- to small-scaleB-fields, and a young-Earth magnetosphere, Kepler-186f and TOI-700d would need minimum planetary magnetic fields of, respectively, 0.05 and 0.24 G. These values are considerably smaller than Earth’s magnetic field of 0.25 G ≲B≲ 0.65 G, which suggests that these two exoplanets might have magnetic fields sufficiently strong to protect their atmospheres and surfaces from stellar magnetic fields. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Astronomy & Astrophysics)
    Context. The Transiting Exoplanet Survey Satellite (TESS) mission is revolutionizing the blossoming area of asteroseismology, particularly of pulsating white dwarfs and pre-white dwarfs, thus continuing the impulse of its predecessor, the Kepler mission. Aims. In this paper, we present the observations from the extended TESS mission in both 120 s short-cadence and 20 s ultra-short-cadence mode of two pre-white dwarf stars showing hydrogen deficiency. We identify them as two new GW Vir stars, TIC 333432673 and TIC 095332541. We apply the tools of asteroseismology with the aim of deriving their structural parameters and seismological distances. Methods. We carried out a spectroscopic analysis and a spectral fitting of TIC 333432673 and TIC 095332541. We also processed and analyzed the high-precision TESS photometric light curves of the two target stars, and derived their oscillation frequencies. We performed an asteroseismological analysis of these stars on the basis of PG 1159 evolutionary models that take into account the complete evolution of the progenitor stars. We searched for patterns of uniform period spacings in order to constrain the stellar mass of the stars. We employed the individual observed periods to search for a representative seismological model. Results. The analysis of the TESS light curves of TIC 333432673 and TIC 095332541 reveals the presence of several oscillations with periods ranging from 350 to 500 s associated to typical gravity ( g )-modes. From follow-up ground-based spectroscopy, we find that both stars have a similar effective temperature ( T eff  = 120 000 ± 10 000 K) and surface gravity (log g  = 7.5 ± 0.5), but a different He/C composition of their atmosphere. On the basis of PG 1159 evolutionary tracks, we derived a spectroscopic mass of M ⋆ = 0.58 −0.08 +0.16   M ⊙ for both stars. Our asteroseismological analysis of TIC 333432673 allowed us to find a constant period spacing compatible with a stellar mass M ⋆  ∼ 0.60 − 0.61  M ⊙ , and an asteroseismological model for this star with a stellar mass M ⋆ = 0.589 ± 0.020 M ⊙ , as well as a seismological distance of d = 459 −156 +188 pc. For this star, we find an excellent agreement between the different methods to infer the stellar mass, and also between the seismological distance and that measured with Gaia ( d Gaia = 389 −5.2 +5.6 pc). For TIC 095332541, we have found a possible period spacing that suggests a stellar mass of M ⋆  ∼ 0.55 − 0.57  M ⊙ . Unfortunately, we have not been able to find an asteroseismological model for this star. Conclusions. Using the high-quality data collected by the TESS space mission and follow-up spectroscopy, we have been able to discover and characterize two new GW Vir stars. The TESS mission is having, and will continue to have, an unprecedented impact on the area of white-dwarf asteroseismology. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email