arXiv subjects

Alessandro Sozzetti

Publications and source records attributed to Alessandro Sozzetti.

At least 55 records · Page 3Linked to original sources

arXiv2021

Atmospheric characterization of terrestrial exoplanets in the mid-infrared: biosignatures, habitability & diversity

Exoplanet science is one of the most thriving fields of modern astrophysics. A major goal is the atmospheric characterization of dozens of small, terrestrial exoplanets in order to search for signatures in their atmospheres that indicate biological activity, assess their ability to provide conditions for life as we know it, and investigate their expected atmospheric diversity. None of the currently adopted projects or missions, from ground or in space, can address these goals. In this White Paper we argue that a large space-based mission designed to detect and investigate thermal emission spectra of terrestrial exoplanets in the MIR wavelength range provides unique scientific potential to address these goals and surpasses the capabilities of other approaches. While NASA might be focusing on large missions that aim to detect terrestrial planets in reflected light, ESA has the opportunity to take leadership and spearhead the development of a large MIR exoplanet mission within the scope of the "Voyage 2050" long-term plan establishing Europe at the forefront of exoplanet science for decades to come. Given the ambitious science goals of such a mission, additional international partners might be interested in participating and contributing to a roadmap that, in the long run, leads to a successful implementation. A new, dedicated development program funded by ESA to help reduce development and implementation cost and further push some of the required key technologies would be a first important step in this direction. Ultimately, a large MIR exoplanet imaging mission will be needed to help answer one of mankind's most fundamental questions: "How unique is our Earth?"

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arXiv2021

Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-Poor K Dwarf

Using radial velocity measurements from four instruments, we report the mass and density of a $2.043\pm0.069 ~\rm{R}_{\oplus}$ sub-Neptune orbiting the quiet K-dwarf Wolf 503 (HIP 67285). In addition, we present improved orbital and transit parameters by analyzing previously unused short-cadence $K2$ campaign 17 photometry and conduct a joint radial velocity-transit fit to constrain the eccentricity at $0.41\pm0.05$. The addition of a transit observation by $Spitzer$ also allows us to refine the orbital ephemeris in anticipation of further follow-up. Our mass determination, $6.26^{+0.69}_{-0.70}~\rm{M}_{\odot}$, in combination with the updated radius measurements, gives Wolf 503 b a bulk density of $ρ= 2.92\pm ^{+0.50}_{-0.44}$ $\rm{g}~\rm{cm}^{-3}$. Using interior composition models, we find this density is consistent with an Earth-like core with either a substantial $\rm{H}_2\rm{O}$ mass fraction ($45^{+19.12}_{-16.15}\%$) or a modest H/He envelope ($0.5\pm0.28\%$). The low H/He mass fraction, along with the old age of Wolf 503 ($11\pm2$ Gyrs), makes this sub-Neptune an opportune subject for testing theories of XUV-driven mass loss while the brightness of its host ($J=8.3$ mag) makes it an attractive target for transmission spectroscopy.

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arXiv2021

The 10 parsec sample in the Gaia era

The nearest stars provide a fundamental constraint for our understanding of stellar physics and the Galaxy. The nearby sample serves as an anchor where all objects can be seen and understood with precise data. This work is triggered by the most recent data release of the astrometric space mission Gaia and uses its unprecedented high precision parallax measurements to review the census of objects within 10 pc. The first aim of this work was to compile all stars and brown dwarfs within 10 pc observable by Gaia, and compare it with the Gaia Catalogue of Nearby Stars as a quality assurance test. We complement the list to get a full 10 pc census, including bright stars, brown dwarfs, and exoplanets. We started our compilation from a query on all objects with a parallax larger than 100 mas using SIMBAD. We completed the census by adding companions, brown dwarfs with recent parallax measurements not in SIMBAD yet, and vetted exoplanets. The compilation combines astrometry and photometry from the recent Gaia Early Data Release 3 with literature magnitudes, spectral types and line-of-sight velocities. We give a description of the astrophysical content of the 10 pc sample. We find a multiplicity frequency of around 28%. Among the stars and brown dwarfs, we estimate that around 61% are M stars and more than half of the M stars are within the range M3.0 V to M5.0 V. We give an overview of the brown dwarfs and exoplanets that should be detected in the next Gaia data releases along with future developments. We provide a catalogue of 540 stars, brown dwarfs, and exoplanets in 339 systems, within 10 pc from the Sun. This list is as volume-complete as possible from current knowledge and provides benchmark stars that can be used, for instance, to define calibration samples and to test the quality of the forthcoming Gaia releases. It also has a strong outreach potential.

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arXiv2021

Five carbon- and nitrogen-bearing species in a hot giant planet's atmosphere

The atmospheres of gaseous giant exoplanets orbiting close to their parent stars (hot Jupiters) have been probed for nearly two decades. They allow us to investigate the chemical and physical properties of planetary atmospheres under extreme irradiation conditions. Previous observations of hot Jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour and carbon monoxide in their atmospheres; this has been studied in terms of scaled solar composition under the usual assumption of chemical equilibrium. Both molecules as well as hydrogen cyanide were found in the atmosphere of HD 209458b, a well studied hot Jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there and subsequently refuted. Here we report observations of HD 209458b that indicate the presence of water (H2O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (CH4), ammonia (NH3) and acetylene (C2H2), with statistical significance of 5.3 to 9.9 standard deviations per molecule. Atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). According to existing models relating the atmospheric chemistry to planet formation and migration scenarios, this would suggest that HD 209458b formed far from its present location and subsequently migrated inwards. Other hot Jupiters may also show a richer chemistry than has been previously found, which would bring into question the frequently made assumption that they have solar-like and oxygen-rich compositions.

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arXiv2020

A celestial matryoshka: Dynamical and spectroscopic analysis of the Albireo system

We present a spectroscopic characterisation and a new orbital solution for the binary system beta Cyg Aa/Ac (MCA 55), the primary component (beta Cyg A) of the well-known wide double star Albireo. By matching evolutionary tracks to the physical parameters of all three Albireo stars (beta Cyg Aa, Ac and B) as obtained from a spectroscopic analysis of TIGRE and IUE spectra, we confirm that they are likely coeval. Our final orbit solution is based on radial-velocity measurements taken over a baseline exceeding $120$ years, combined with relative astrometry from speckle interferometric observations and the absolute astrometry from the Hipparcos and Gaia missions. Our final orbit solution has a period of $121.65^{+3.34}_{-2.90}$ years with an eccentricity of $0.20^{+0.01}_{-0.02}$. Thanks to the inclusion of the absolute astrometry, we find a mass ratio of $q = 1.25^{+0.19}_{-0.17}$, and a total mass of $9.47_{-3.24}^{+5.88}$ M$_\odot$, indicating that the secondary (Ac) is the more massive of the pair. These results strongly suggest the presence of a fourth, unseen, member of the Albireo system. Given the current photometric data it is likely that beta Cyg A is itself a hierarchical triple. We also derive the systemic proper motion, line-of-sight velocity, and an orbital parallax of the beta Cyg A system, allowing us to quantitatively assess the hypothesis that Albireo A and B form a physically bound and genealogically connected system. Finally, we find four potential members of a common proper motion group with Albireo, though none anywhere as close by as the Albireo components A to B.

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arXiv2020

The GAPS Programme at TNG XXVIII -- A pair of hot-Neptunes orbiting the young star TOI-942

Both young stars and multi-planet systems are primary objects that allow us to study, understand and constrain planetary formation and evolution theories. We validate the physical nature of two Neptune-type planets transiting TOI-942 (TYC 5909-319-1), a previously unacknowledged young star (50+30-20 Myr) observed by the TESS space mission in Sector 5. Thanks to a comprehensive stellar characterization, TESS light curve modelling and precise radial-velocity measurements, we validated the planetary nature of the TESS candidate and detect an additional transiting planet in the system on a larger orbit. From photometric and spectroscopic observations we performed an exhaustive stellar characterization and derived the main stellar parameters. TOI-942 is a relatively active K2.5V star (logR'hk = -4.17+-0.01) with rotation period Prot = 3.39+-0.01 days, a projected rotation velocity vsini=13.8+-0.5 km/s and a radius of ~0.9 Rsun. We found that the inner planet, TOI-942b, has an orbital period Pb=4.3263+-0.0011 days, a radius Rb=4.242-0.313+0.376 Rearth and a mass upper limit of 16 Mearth at 1-sigma confidence level. The outer planet, TOI-942c, has an orbital period Pc=10.1605-0.0053+0.0056 days, a radius Rc=4.793-0.351+0.410 Rearth and a mass upper limit of 37 Mearth at 1-sigma confidence level.

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arXiv2020

Fundamental physics with Espresso: Towards an accurate wavelength calibration for a precision test of the fine-structure constant

Observations of metal absorption systems in the spectra of distant quasars allow to constrain a possible variation of the fine-structure constant throughout the history of the Universe. Such a test poses utmost demands on the wavelength accuracy and previous studies were limited by systematics in the spectrograph wavelength calibration. A substantial advance in the field is therefore expected from the new ultra-stable high-resolution spectrograph Espresso, recently installed at the VLT. In preparation of the fundamental physics related part of the Espresso GTO program, we present a thorough assessment of the Espresso wavelength accuracy and identify possible systematics at each of the different steps involved in the wavelength calibration process. Most importantly, we compare the default wavelength solution, based on the combination of Thorium-Argon arc lamp spectra and a Fabry-Pérot interferometer, to the fully independent calibration obtained from a laser frequency comb. We find wavelength-dependent discrepancies of up to 24m/s. This substantially exceeds the photon noise and highlights the presence of different sources of systematics, which we characterize in detail as part of this study. Nevertheless, our study demonstrates the outstanding accuracy of Espresso with respect to previously used spectrographs and we show that constraints of a relative change of the fine-structure constant at the $10^{-6}$ level can be obtained with Espresso without being limited by wavelength calibration systematics.

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arXiv2020

ARES IV: Probing the atmospheres of the two warm small planets HD 106315 c and HD 3167 c with the HST/WFC3 camera

We present an atmospheric characterization study of two medium sized planets bracketing the radius of Neptune: HD 106315 c (R$_{\rm{P}}$=4.98 $\pm$ 0.23 R$_{\oplus}$) and HD 3167 c (R$_{\rm{P}}$=2.740$_{-0.100}^{+0.106}$ R$_{\oplus}$). We analyse spatially scanned spectroscopic observations obtained with the G141 grism (1.125 - 1.650 $μ$m) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. We use the publicly available Iraclis pipeline and TauREx3 atmospheric retrieval code and we detect water vapor in the atmosphere of both planets with an abundance of $\log_{10}[\mathrm{H_2O}]=-2.1^{+0.7}_{-1.3}$ ($\sim$5.68$σ$) and $\log_{10}[\mathrm{H_2O}]=-4.1^{+0.9}_{-0.9}$ ($\sim$3.17$σ$) for HD 106315 c and HD 3167 c, respectively. The transmission spectrum of HD 106315 c shows also a possible evidence of ammonia absorption ($\log_{10}[\mathrm {NH_3}]=-4.3^{+0.7}_{-2.0}$, $\sim$1.97$σ$ -even if it is not significant-), whilst carbon dioxide absorption features may be present in the atmosphere of HD 3167 c in the $\sim$1.1-1.6~$μ$m wavelength range ($\log_{10}[\mathrm{CO_{2}}]= -2.4^{+0.7}_{-1.0}$, $\sim$3.28$σ$). However the CO$_2$ detection appears significant, it must be considered carefully and put into perspective. Indeed, CO$_2$ presence is not explained by 1D equilibrium chemistry models, and it could be due to possible systematics. The additional contribution of clouds, CO and CH$_4$ are discussed. HD 106315 c and HD 3167 c will be interesting targets for upcoming telescopes such as the James Webb Space Telescope (JWST) and the Atmospheric Remote-Sensing Infrared Exoplanet Large-Survey (Ariel).

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arXiv2020

Statistical properties of habitable zones in stellar binary systems

Observations of exoplanets and protoplanetary disks show that binary stellar systems can host planets in stable orbits. Given the high binary fraction among stars, the contribution of binary systems to Galactic habitability should be quantified. Therefore, we have designed a suite of Monte Carlo experiments aimed at generating large (up to $10^6$) samples of binary systems. For each system randomly extracted we calculate the intersection between the radiative habitable zones and the regions of dynamical stability using published empirical formulations that account for the dynamical and radiative parameters of both stars of the system. We also consider constraints on planetary formation in binary systems. We find that the habitability properties of circumstellar and circumbinary regions are quite different and complementary with respect to the binary system parameters. Circumbinary HZs are, generally, rare ($\simeq 4\%$) in the global population of binary systems, even if they are common for stellar separations $\lesssim 0.2$ AU. Conversely, circumstellar HZs are frequent ($\ge 80\%$) in the global population, but are rare for stellar separations $\lesssim 1$ AU. These results are robust against variations of poorly constrained binary systems parameters. We derive ranges of stellar separations and stellar masses for which HZs in binary systems can be wider than the HZs around single stars; the widening can be particularly strong (up to one order of magnitude) for circumstellar regions around M-type secondary stars. The comparison of our statistical predictions with observational surveys shows the impact of selection effects on the habitability properties of detected exoplanets in binary systems.

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arXiv2020

TOI-1235 b: a keystone super-Earth for testing radius valley emergence models around early M dwarfs

Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally-driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/non-rocky transition in period-radius space. Here we present the confirmation of TOI-1235 b ($P=3.44$ days, $r_p=1.738^{+0.087}_{-0.076}$ R$_{\oplus}$), a planet whose size and period are intermediate between the competing model predictions thus making the system an important test case for emergence models of the rocky/non-rocky transition around early M dwarfs ($R_s=0.630\pm 0.015$ R$_{\odot}$, $M_s=0.640\pm 0.016$ M$_{\odot}$). We confirm the TESS planet discovery using reconnaissance spectroscopy, ground-based photometry, high-resolution imaging, and a set of 38 precise radial-velocities from HARPS-N and HIRES. We measure a planet mass of $6.91^{+0.75}_{-0.85}$ M$_{\oplus}$, which implies an iron core mass fraction of $20^{+15}_{-12}$% in the absence of a gaseous envelope. The bulk composition of TOI-1235 b is therefore consistent with being Earth-like and we constrain a H/He envelope mass fraction to be $<0.5$% at 90% confidence. Our results are consistent with model predictions from thermally-driven atmospheric mass loss but not with gas-poor formation, suggesting that the former class of processes remain efficient at sculpting close-in planets around early M dwarfs. Our RV analysis also reveals a strong periodicity close to the first harmonic of the photometrically-determined stellar rotation period that we treat as stellar activity, despite other lines of evidence favoring a planetary origin ($P=21.8^{+0.9}_{-0.8}$ days, $m_p\sin{i}=13.0^{+3.8}_{-5.3}$ M$_{\oplus}$) that cannot be firmly ruled out by our data.

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arXiv2020

A pair of TESS planets spanning the radius valley around the nearby mid-M dwarf LTT 3780

We present the confirmation of two new planets transiting the nearby mid-M dwarf LTT 3780 (TIC 36724087, TOI-732, $V=13.07$, $K_s=8.204$, $R_s$=0.374 R$_{\odot}$, $M_s$=0.401 M$_{\odot}$, d=22 pc). The two planet candidates are identified in a single TESS sector and are validated with reconnaissance spectroscopy, ground-based photometric follow-up, and high-resolution imaging. With measured orbital periods of $P_b=0.77$ days, $P_c=12.25$ days and sizes $r_{p,b}=1.33\pm 0.07$ R$_{\oplus}$, $r_{p,c}=2.30\pm 0.16$ R$_{\oplus}$, the two planets span the radius valley in period-radius space around low mass stars thus making the system a laboratory to test competing theories of the emergence of the radius valley in that stellar mass regime. By combining 63 precise radial-velocity measurements from HARPS and HARPS-N, we measure planet masses of $m_{p,b}=2.62^{+0.48}_{-0.46}$ M$_{\oplus}$ and $m_{p,c}=8.6^{+1.6}_{-1.3}$ M$_{\oplus}$, which indicates that LTT 3780b has a bulk composition consistent with being Earth-like, while LTT 3780c likely hosts an extended H/He envelope. We show that the recovered planetary masses are consistent with predictions from both photoevaporation and from core-powered mass loss models. The brightness and small size of LTT 3780, along with the measured planetary parameters, render LTT 3780b and c as accessible targets for atmospheric characterization of planets within the same planetary system and spanning the radius valley.

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arXiv2020

Molecular Cross Sections for High Resolution Spectroscopy of Super Earths, Warm Neptunes and Hot Jupiters

High resolution spectroscopy (HRS) has been used to detect a number of species in the atmospheres of hot Jupiters. Key to such detections is accurately and precisely modelled spectra for cross-correlation against the R$\gtrsim$20,000 observations. There is a need for the latest generation of opacities which form the basis for high signal-to-noise detections using such spectra. In this study we present and make publicly available cross sections for six molecular species, H$_2$O, CO, HCN, CH$_4$, NH$_3$ and CO$_2$ using the latest line lists most suitable for low- and high-resolution spectroscopy. We focus on the infrared (0.95-5~$μ$m) and between 500-1500~K where these species have strong spectral signatures. We generate these cross sections on a grid of pressures and temperatures typical for the photospheres of super Earth, warm Neptunes and hot Jupiters using the latest H$_2$ and He pressure broadening. We highlight the most prominent infrared spectral features by modelling three representative exoplanets, GJ~1214~b, GJ~3470~b and HD~189733~b, which encompass a wide range in temperature, mass and radii. In addition, we verify the line lists for H$_2$O, CO and HCN with previous high resolution observations of hot Jupiters. However, we are unable to detect CH$_4$ with our new cross sections from HRS observations of HD~102195~b. These high accuracy opacities are critical for atmospheric detections with HRS and will be continually updated as new data becomes available.

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arXiv2020

Nightside condensation of iron in an ultra-hot giant exoplanet

Ultra-hot giant exoplanets receive thousands of times Earth's insolation. Their high-temperature atmospheres (>2,000 K) are ideal laboratories for studying extreme planetary climates and chemistry. Daysides are predicted to be cloud-free, dominated by atomic species and substantially hotter than nightsides. Atoms are expected to recombine into molecules over the nightside, resulting in different day-night chemistry. While metallic elements and a large temperature contrast have been observed, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ("evening") and night-to-day ("morning") terminators could, however, be revealed as an asymmetric absorption signature during transit. Here, we report the detection of an asymmetric atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this signature thanks to the combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. Iron must thus condense during its journey across the nightside.

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arXiv2019

An 11 Earth-Mass, Long-Period Sub-Neptune Orbiting a Sun-like Star

Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with M_* = 0.892 +/- (0.051, 0.035) M_sun and R_* = 0.8717 +/- (0.0064, 0.0061) R_sun. Kepler-538b is a 2.215 +/- (0.040, 0.034) R_earth sub-Neptune with a period of P = 81.73778 +/- 0.00013 d. It is the only known planet in the system. We collected radial velocity (RV) observations with HIRES on Keck I and HARPS-N on the TNG. We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross correlation function full width at half maximum (FWHM) observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K = 1.68 +/- (0.39, 0.38) m s^-1 and a planet mass of M_p = 10.6 +/- (2.5, 2.4) M_earth. Kepler-538b is the smallest planet beyond P = 50 d with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.

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arXiv2019

Using HARPS-N to characterise the long-period planets in the PH-2 and Kepler-103 systems

We present confirmation of the planetary nature of PH-2b, as well as the first mass estimates for the two planets in the Kepler-103 system. PH-2b and Kepler-103c are both long-period and transiting, a sparsely-populated category of exoplanet. We use {\it Kepler} light-curve data to estimate a radius, and then use HARPS-N radial velocities to determine the semi-amplitude of the stellar reflex motion and, hence, the planet mass. For PH-2b we recover a 3.5-$σ$ mass estimate of $M_p = 109^{+30}_{-32}$ M$_\oplus$ and a radius of $R_p = 9.49\pm0.16$ R$_\oplus$. This means that PH-2b has a Saturn-like bulk density and is the only planet of this type with an orbital period $P > 200$ days that orbits a single star. We find that Kepler-103b has a mass of $M_{\text{p,b}} = 11.7^{+4.31}_{-4.72}$ M$_{\oplus}$ and Kepler-103c has a mass of $M_{\text{p,c}} = 58.5^{+11.2}_{-11.4}$ M$_{\oplus}$. These are 2.5$σ$ and 5$σ$ results, respectively. With radii of $R_{\text{p,b}} = 3.49^{+0.06}_{-0.05}$ R$_\oplus$, and $R_{\text{p,c}} = 5.45^{+0.18}_{-0.17}$ R$_\oplus$, these results suggest that Kepler-103b has a Neptune-like density, while Kepler-103c is one of the highest density planets with a period $P > 100$ days. By providing high-precision estimates for the masses of the long-period, intermediate-mass planets PH-2b and Kepler-103c, we increase the sample of long-period planets with known masses and radii, which will improve our understanding of the mass-radius relation across the full range of exoplanet masses and radii.

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arXiv2019

ESA Voyage 2050 White Paper: Detecting life outside our solar system with a large high-contrast-imaging mission

In this white paper, we recommend the European Space Agency plays a proactive role in developing a global collaborative effort to construct a large high-contrast imaging space telescope, e.g. as currently under study by NASA. Such a mission will be needed to characterize a sizable sample of temperate Earth-like planets in the habitable zones of nearby Sun-like stars and to search for extraterrestrial biological activity. We provide an overview of relevant European expertise, and advocate ESA to start a technology development program towards detecting life outside the Solar system.

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arXiv2019

Voyage 2050 White Paper: All-Sky Visible and Near Infrared Space Astrometry

A new all-sky visible and Near-InfraRed (NIR) space astrometry mission with a wavelength cutoff in the K-band is not just focused on a single or small number of key science cases. Instead, it is extremely broad, answering key science questions in nearly every branch of astronomy while also providing a dense and accurate visible-NIR reference frame needed for future astronomy facilities. For almost 2 billion common stars the combination of Gaia and a new all-sky NIR astrometry mission would provide much improved proper motions, answering key science questions -- from the solar system and stellar systems, including exoplanet systems, to compact galaxies, quasars, neutron stars, binaries and dark matter substructures. The addition of NIR will result in up to 8 billion newly measured stars in some of the most obscured parts of our Galaxy, and crucially reveal the very heart of the Galactic bulge region. In this white paper we argue that rather than improving on the accuracy, a greater overall science return can be achieved by going deeper than Gaia and by expanding the wavelength range to the NIR.

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arXiv2019

The Revised TESS Input Catalog and Candidate Target List

We describe the catalogs assembled and the algorithms used to populate the revised TESS Input Catalog (TIC), based on the incorporation of the Gaia second data release. We also describe a revised ranking system for prioritizing stars for 2-minute cadence observations, and assemble a revised Candidate Target List (CTL) using that ranking. The TIC is available on the Mikulski Archive for Space Telescopes (MAST) server, and an enhanced CTL is available through the Filtergraph data visualization portal system at the URL http://filtergraph.vanderbilt.edu/tess_ctl.

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