Nearly every massive galaxy harbors a supermassive black hole (SMBH) in its nucleus. SMBH masses are millions to billions of solar mass, and they correlate with properties of spheroids of their host ...galaxies. While the SMBH growth channels, mergers, and gas accretion are well established, their origin remains uncertain: they could have emerged either from massive "seeds" (105-106 M ) formed by direct collapse of gas clouds in the early universe or from smaller (100 M ) BHs, end products of first stars. The latter channel would leave behind numerous intermediate-mass BHs (IMBHs, 102-105 M ). Although many IMBH candidates have been identified, none are accepted as definitive; thus, their very existence is still debated. Using data mining in wide-field sky surveys and applying dedicated analysis to archival and follow-up optical spectra, we identified a sample of 305 IMBH candidates having masses 3 × 10 4 M < M BH < 2 × 10 5 M , which reside in galaxy centers and are accreting gas that creates characteristic signatures of a type I active galactic nucleus (AGN). We confirmed the AGN nature of 10 sources (including five previously known objects that validate our method) by detecting the X-ray emission from their accretion disks, thus defining the first bona fide sample of IMBHs in galactic nuclei. All IMBH host galaxies possess small bulges and sit on the low-mass extension of the M BH - M bulge scaling relation, suggesting that they must have experienced very few if any major mergers over their lifetime. The very existence of nuclear IMBHs supports the stellar-mass seed scenario of the massive BH formation.
ABSTRACT GJ 1214b is the most studied sub-Neptune exoplanet to date. Recent measurements have shown its near-infrared transmission spectrum to be flat, pointing to a high-altitude opacity source in ...the exoplanet's atmosphere, either equilibrium condensate clouds or photochemical hazes. Many photometric observations have been reported in the optical by different groups, though simultaneous measurements spanning the entire optical regime are lacking. We present an optical transmission spectrum (4500-9260 ) of GJ 1214b in 14 bins, measured with Magellan/IMACS repeatedly over three transits. We measure a mean planet-to-star radius ratio of R p / R s = 0.1146 2 × 10 − 4 and mean uncertainty of ( R p / R s ) = 8.7 × 10 − 4 in the spectral bins. The optical transit depths are shallower on average than observed in the near-infrared. We present a model for jointly incorporating the effects of a composite photosphere and atmospheric transmission through the exoplanet's limb (the CPAT model), and use it to examine the cases of absorber and temperature heterogeneities in the stellar photosphere. We find the optical and near-infrared measurements are best explained by the combination of (1) photochemical haze in the exoplanetary atmosphere with a mode particle size r = 0.1 m and haze-forming efficiency f haze = 10 % and (2) faculae in the unocculted stellar disk with a temperature contrast Δ T = 354 − 46 + 46 K, assuming 3.2% surface coverage. The CPAT model can be used to assess potential contributions of heterogeneous stellar photospheres to observations of exoplanet transmission spectra, which will be important for searches for spectral features in the optical.
Abstract
We present new optical transmission spectra for two hot Jupiters: WASP-25b (
M
= 0.56
M
J
;
R
= 1.23
R
J
;
P
= 3.76 days) and WASP-124b (
M
= 0.58
M
J
;
R
= 1.34
R
J
;
P
= 3.37 days), with ...wavelength coverages of 4200–9100 Å and 4570–9940 Å, respectively. These spectra are from the ESO Faint Object Spectrograph and Camera (v.2) mounted on the New Technology Telescope and Inamori-Magellan Areal Camera & Spectrograph on Magellan Baade. No strong spectral features were found in either spectra, with the data probing 4 and 6 scale heights, respectively.
Exoretrievals
and
PLATON
retrievals favor stellar activity for WASP-25b, while the data for WASP-124b did not favor one model over another. For both planets the retrievals found a wide range in the depths where the atmosphere could be optically thick (∼0.4
μ
–0.2 bars for WASP-25b and 1.6
μ
–32 bars for WASP-124b) and recovered a temperature that is consistent with the planets’ equilibrium temperatures, but with wide uncertainties (up to ±430 K). For WASP-25b, the models also favor stellar spots that are ∼500–3000 K cooler than the surrounding photosphere. The fairly weak constraints on parameters are owing to the relatively low precision of the data, with an average precision of 840 and 1240 ppm per bin for WASP-25b and WASP-124b, respectively. However, some contribution might still be due to an inherent absence of absorption or scattering in the planets’ upper atmospheres, possibly because of aerosols. We attempt to fit the strength of the sodium signals to the aerosol–metallicity trend proposed by McGruder et al., and find WASP-25b and WASP-124b are consistent with the prediction, though their uncertainties are too large to confidently confirm the trend.
We present photometry of four transits of the exoplanet WASP-4b, each with a precision of approximately 500 ppm and a time sampling of 40-60 s. We have used the data to refine the estimates of the ...system parameters and ephemerides. During two of the transits we observed a short-lived, low-amplitude anomaly that we interpret as the occultation of a starspot by the planet. We also found evidence for a pair of similar anomalies in previously published photometry. The recurrence of these anomalies suggests that the stellar rotation axis is nearly aligned with the orbital axis, or else the starspot would not have remained on the transit chord. By analyzing the timings of the anomalies we find the sky-projected stellar obliquity to be Delta *l = --1+14 -- 12 degrees. This result is consistent with (and more constraining than) a recent observation of the Rossiter-McLaughlin effect. It suggests that the planet migration mechanism preserved the initially low obliquity, or else that tidal evolution has realigned the system. Future applications of this method using data from the CoRoT and Kepler missions will allow spin-orbit alignment to be probed for many other exoplanets.
Abstract
We present a new ground-based optical transmission spectrum of the ultrahot Jupiter WASP-103b (
T
eq
=
2484
K). Our transmission spectrum is the result of combining five new transits from ...the ACCESS survey and two new transits from the LRG-BEASTS survey with a reanalysis of three archival Gemini/GMOS transits and one VLT/FORS2 transit. Our combined 11-transit transmission spectrum covers a wavelength range of 3900–9450 Å with a median uncertainty in the transit depth of 148 parts per million, which is less than one atmospheric scale height of the planet. In our retrieval analysis of WASP-103b’s combined optical and infrared transmission spectrum, we find strong evidence for unocculted bright regions (4.3
σ
) and weak evidence for H
2
O (
1.9
σ
), HCN (
1.7
σ
), and TiO (
2.1
σ
), which could be responsible for WASP-103b’s observed temperature inversion. Our optical transmission spectrum shows significant structure that is in excellent agreement with the extensively studied ultrahot Jupiter WASP-121b, for which the presence of VO has been inferred. For WASP-103b, we find that VO can only provide a reasonable fit to the data if its abundance is implausibly high and we do not account for stellar activity. Our results highlight the precision that can be achieved by ground-based observations and the impacts that stellar activity from F-type stars can have on the interpretation of exoplanet transmission spectra.
We present medium-resolution optical (lambda/ Delta lambda ~ 4000) and near-infrared (lambda/ Delta lambda ~ 8000) spectral data for components of the newly discovered WISE J104915.57-531906.1 AB ...(Luhman 16AB) brown dwarf binary. Compared to the strength of K I line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J-band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 mu m and 1.25 mu m regions than Luhman 16A. We calculate bolometric luminosities from observed data supplemented with best fit models for longer wavelengths and find the components are consistent within la with resultant T sub(effs) of 1310 + or - 30 K and 1280 + or - 75 K for Luhman 16AB respectively.
We present a new optical (400-950 nm) transmission spectrum of the hot Jupiter WASP-31b (M = 0.48 MJ; R = 1.54 RJ; P = 3.41 days), obtained by combining four transit observations. These transits were ...observed with IMACS on the Magellan Baade Telescope at Las Campanas Observatory as part of the ACCESS project. We investigate the presence of clouds/hazes in the upper atmosphere of this planet, as well as the contribution of stellar activity on the observed features. In addition, we search for absorption features of the alkali elements Na i and K i, with particular focus on K i, for which there have been two previously published disagreeing results. Observations with Hubble Space Telescope (HST)/STIS detected K i, whereas ground-based low- and high-resolution observations did not. We use equilibrium and nonequilibrium chemistry retrievals to explore the planetary and stellar parameter space of the system with our optical data combined with existing near-IR observations. Our best-fit model is that with a scattering slope consistent with a Rayleigh slope ( ), high-altitude clouds at a log cloud top pressure of −3.6 bars, and possible muted H2O features. We find that our observations support other ground-based claims of no K i. Clouds are likely why signals like H2O are extremely muted and Na or K cannot be detected. We then juxtapose our Magellan/IMACS transmission spectrum with existing VLT/FORS2, HST/WFC3, HST/STIS, and Spitzer observations to further constrain the optical-to-infrared atmospheric features of the planet. We find that a steeper scattering slope ( = 8.3 1.5) is anchored by STIS wavelengths blueward of 400 nm and only the original STIS observations show significant potassium signal.
Abstract
We present a new ground-based visible transmission spectrum of the high-gravity, hot Jupiter HAT-P-23b, obtained as part of the ACCESS project. We derive the spectrum from five transits ...observed between 2016 and 2018, with combined wavelength coverage between 5200 Å and 9269 Å in 200 Å bins, and with a median precision of 247 ppm per bin. HAT-P-23b’s relatively high surface gravity (
g
≈ 30 m s
−2
), combined with updated stellar and planetary parameters from Gaia DR2, gives a five-scale-height signal of 384 ppm for a hydrogen-dominated atmosphere. Bayesian models favor a clear atmosphere for the planet with the tentative presence of TiO, after simultaneously modeling stellar contamination, using spots parameter constraints from photometry. If confirmed, HAT-P-23b would be the first example of a high-gravity gas giant with a clear atmosphere observed in transmission at optical/near-IR wavelengths; therefore, we recommend expanding observations to the UV and IR to confirm our results and further characterize this planet. This result demonstrates how combining transmission spectroscopy of exoplanet atmospheres with long-term photometric monitoring of the host stars can help disentangle the exoplanet and stellar activity signals.
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