The PHOENIX Exoplanet Retrieval Algorithm and Using H−^{-} Opacity as a Probe in Ultra-hot Jupiters

Atmospheric retrievals are now a standard tool to analyze observations of exoplanet atmospheres. This data-driven approach quantitatively compares atmospheric models to observations in order to estimate atmospheric properties and their uncertainties. In this paper, we introduce a new retrieval package, the PHOENIX Exoplanet Retrieval Analysis (PETRA). PETRA places the PHOENIX atmosphere model in a retrieval framework, allowing us to combine the strengths of a well-tested and widely-used atmosphere model with the advantages of retrieval algorithms. We validate PETRA by retrieving on simulated data for which the true atmospheric state is known. We also show that PETRA can successfully reproduce results from previously published retrievals of WASP-43b and HD 209458b. For the WASP-43b results, we show the effect that different line lists and line profile treatments have on the retrieved atmospheric properties. Lastly, we describe a novel technique for retrieving the temperature structure and $e^{-}$ density in ultra-hot Jupiters using H$^{-}$ opacity, allowing us to probe atmospheres devoid of most molecular features with JWST.Comment: 17 pages, 18 figures. Accepted for publication in A

Extremely Irradiated Hot Jupiters: Non-Oxide Inversions, H- Opacity, and Thermal Dissociation of Molecules

Extremely irradiated hot Jupiters, exoplanets reaching dayside temperatures ${>}$2000 K, stretch our understanding of planetary atmospheres and the models we use to interpret observations. While these objects are planets in every other sense, their atmospheres reach temperatures at low pressures comparable only to stellar atmospheres. In order to understand our \textit{a priori} theoretical expectations for the nature of these objects, we self-consistently model a number of extreme hot Jupiter scenarios with the PHOENIX model atmosphere code. PHOENIX is well-tested on objects from cool brown dwarfs to expanding supernovae shells and its expansive opacity database from the UV to far-IR make PHOENIX well-suited for understanding extremely irradiated hot Jupiters. We find several fundamental differences between hot Jupiters at temperatures ${>}$2500 K and their cooler counterparts. First, absorption by atomic metals like Fe and Mg, molecules including SiO and metal hydrides, and continuous opacity sources like H$^-$ all combined with the short-wavelength output of early-type host stars result in strong thermal inversions, without the need for TiO or VO. Second, many molecular species, including H$_2$O, TiO, and VO are thermally dissociated at pressures probed by eclipse observations, biasing retrieval algorithms that assume uniform vertical abundances. We discuss other interesting properties of these objects, as well as future prospects and predictions for observing and characterizing this unique class of astrophysical object, including the first self-consistent model of the hottest known jovian planet, KELT-9b.Comment: 23 pages, 16 figures, 1 table. Submitted to Ap

The Influence of Host Star Spectral Type on Ultra-Hot Jupiter Atmospheres

Ultra-hot Jupiters are the most highly irradiated gas giant planets, with equilibrium temperatures from 2000 to over 4000 K. Ultra-hot Jupiters are amenable to characterization due to their high temperatures, inflated radii, and short periods, but their atmospheres are atypical for planets in that the photosphere possesses large concentrations of atoms and ions relative to molecules. Here we evaluate how the atmospheres of these planets respond to irradiation by stars of different spectral type. We find that ultra-hot Jupiters exhibit temperature inversions that are sensitive to the spectral type of the host star. The slope and temperature range across the inversion both increase as the host star effective temperature increases due to enhanced absorption at short wavelengths and low pressures. The steep temperature inversions in ultra-hot Jupiters around hot stars result in increased thermal dissociation and ionization compared to similar planets around cooler stars. The resulting increase in H$^{-}$ opacity leads to a transit spectrum that has muted absorption features. The emission spectrum, however, exhibits a large contrast in brightness temperature, a signature that will be detectable with both secondary eclipse observations and high-dispersion spectroscopy. We also find that the departures from local thermodynamic equilibrium in the stellar atmosphere can affect the degree of heating caused by atomic metals in the planet's upper atmosphere. Additionally, we further quantify the significance of heating by different opacity sources in ultra-hot Jupiter atmospheres.Comment: 13 pages, 9 figures, 2 tables. Accepted for publication in Ap

Evaluation of the use of an academic integrity training course as a proactive measure encouraging academic honesty

Significant research has been conducted exploring many aspects of academic integrity including the role of an academic honor code. Although academic institutions have created courses and training programs detailing expected academic standards, no published empirical evidence supporting the reliability or validity of such efforts could be located. The purpose of this study was to gather evidence documenting the effectiveness of the Metropolitan Community College Academic Integrity Training Course (MCC AITC). This objective was the cornerstone influencing the research design that included the creation of a treatment mechanism (AITC) consisting of five module quizzes, one pretest, two posttests (posttest1, posttest2), and various evaluation tools.;The MCC Business Administration Department was selected to pilot the AITC, and, for comparative purposes, the Social Sciences Department was also asked to participate. Using student rosters from eight classes (four Finance and four Psychology), 154 students were randomly assigned to either group WA or group WB. A total of 86 students completed the AITC that was conducted during the Spring 2008 academic quarter. Pearson chi-square tests reported no significant difference between participants and nonparticipants specific to group or class; T-tests, however, revealed there were statistically significant differences between groups (WA and WB) with respect to GPA, and classes (Finance and Psychology) specific to credits attempted and completed.;The AITC was delivered online using WebCT where students were provided limited accessibility (Day1: 1 login per student; Day14: 1 login per student). Once logged in, students were expected to finish the course requirements in their entirety (Day1: pretest, modules 1--5, and posttest1; Day14: posttest2). Estimated completion time on Day1 was 90 minutes and on Day14 10 minutes. Measurement instruments assessed learning based on three constructs: knowledge, understanding, and attitude. Numerous subscales were developed to evaluate the measurement instruments (pretest, module quizzes, and posttests) created to assess the constructs of knowledge, understanding, and attitude. Cronbach\u27s alpha results indicated the use of the subscales developed to measure attitude were reliable measures; subscales created to measure knowledge and understanding, however, may not have been reliable. Similarly, results assessing the internal consistency of the individual module scores suggested these scales may also not have been reliable. As exploratory research, the cumulative module scale was considered reliable given a lower accepted cut-off value.;Data analysis tools also included the use of Pearson chi-square tests, T-tests, repeated-measures 2 x 2 x 3 ANOVA, and pairwise comparisons. Results from pretest and posttests suggest participation in the AITC did significantly enhance student knowledge and understanding of concepts and expectations of ethical behavior in the classroom; changes specific to knowledge, however, were not sustained over time. Research also revealed a statistically significant relationship between module quiz scores and correct responses to knowledge questions (posttest1) as well as understanding questions (posttest 1, posttest2). Further, analysis specific to module quizzes revealed participation in the AITC did significantly enhance student knowledge and understanding of potential penalties imposed given the occurrence of a violation as well as student understanding of the relationship between academic integrity and workplace integrity.;To encourage academic integrity, colleges and universities are creating courses and training programs detailing expected academic standards. With the exception of this study, it is believed no published empirical evidence supporting the reliability or validity of these efforts exists. Although this study can be considered valid in that it provided evidence documenting the effectiveness of the AITC, threats and biases potentially undermining the validity of this study (e.g., statistical, construct, content, and internal validity) should be considered. Consequently, the reader is advised to review these findings in consideration of said limitations. Suggested future research efforts based on these findings include those addressing identified limitations as well as studies evaluating the long-term value of an academic integrity training course. Until further research is conducted, those in the academic community are left to question the real value of academic integrity training

Pre- and Post-matriculation Demographic and Academic Profiles of Undergraduate Hispanic Students: A Single Institution Case Study

This study sought to identify pre- and post-matriculation characteristics of undergraduate Hispanic students at the University of North Texas (UNT). The study also examined demographic trends among this population. Eleven purposes guided the study: 1) to determine geographic origins of the undergraduate Hispanic students at UNT in terms of location of educational institution attended prior to matriculation; 2) to establish whether students entered UNT as true freshmen or transfer students; 3) to ascertain the gender composition of undergraduate Hispanic students at UNT; 4) to report the highest level of education achieved by parents of undergraduate Hispanic students at UNT; 5) to explore patterns in major selection of undergraduate Hispanic students at UNT and who or what influenced that choice of major; 6) to ascertain the percentage of undergraduate Hispanic students at UNT who plan to use financial aid during their enrollment; 7) to examine the graduation rates among undergraduate Hispanic students at UNT; 8) to determine who is most influential in the academic decisions made by Hispanic undergraduate students at UNT; 9) to discover what type of emotional support is given to Hispanic students pertaining to their college enrollment and success; 10) to establish why Hispanic undergraduate students elect to attend UNT; and 11) to discover what factors prohibit new undergraduate Hispanic students at UNT from graduating. Data were collected from undergraduate Hispanic students attending spring 2003 orientation using a new-student survey instrument. Additional data were collected using UNT student information system reports. Chi-square statistics were performed to identify significant results. Results of the study indicated both characteristics substantiated in previous research and characteristics unique to this sample existed among the undergraduate Hispanic students at UNT. The results, particularly as concerned with the parental influence exerted on students in the study, departed from the finding of past research. Additional research on this population was warranted and suggested

An HST/STIS Optical Transmission Spectrum of Warm Neptune GJ 436b

GJ 436b is a prime target for understanding warm Neptune exoplanet atmospheres and a target for multiple JWST GTO programs. Here, we report the first space-based optical transmission spectrum of the planet using two HST/STIS transit observations from 0.53-1.03 microns. We find no evidence for alkali absorption features, nor evidence of a scattering slope longward of 0.53 microns. The spectrum is indicative of moderate to high metallicity (~100-1000x solar) while moderate metallicity scenarios (~100x solar) require aerosol opacity. The optical spectrum also rules out some highly scattering haze models. We find an increase in transit depth around 0.8 microns in the transmission spectra of 3 different sub-Jovian exoplanets (GJ 436b, HAT-P-26b, and GJ 1214b). While most of the data come from STIS, data from three other instruments may indicate this is not an instrumental effect. Only the transit spectrum of GJ 1214b is well fit by a model with stellar plages on the photosphere of the host star. Our photometric monitoring of the host star reveals a stellar rotation rate of 44.1 days and an activity cycle of 7.4 years. Intriguingly, GJ 436 does not become redder as it gets dimmer, which is expected if star spots were dominating the variability. These insights into the nature of the GJ 436 system help refine our expectations for future observations in the era of JWST, whose higher precision and broader wavelength coverage will shed light on the composition and structure of GJ 436b's atmosphere.Comment: 20 pages, 11 figures, 5 tables, Accepted to AJ. A full version of table 1 is included as table1_mrt.tx

The Effect of 3D Transport-induced Disequilibrium Carbon Chemistry on the Atmospheric Structure, Phase Curves, and Emission Spectra of Hot Jupiter HD 189733b

On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH4 and CO much faster than chemical reactions restore chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested to explain discrepancies between observed infrared light curves and those predicted by GCMs. On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer. 4.5 mu m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH4, CO, and H2O by assuming that the CH4/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with eight CH4/CO ratios. In the more likely CO-dominated regime, we find temperature changes. >= 50-100 K compared to the simulation for equilibrium chemistry across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures between 600 and 1300 K. We find that spectra in regions with strong methane absorption, including the Spitzer. 3.6 and 8 mu m bands, are strongly impacted by disequilibrium abundances. We expect chemical quenching to result in much larger nightside fluxes in the 3.6 mu m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 mu m band, because the changes in opacity due to CO and H2O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 mu m band.NASA Origins grant [NNX12AI79G]; NASA Headquarters under the NASA Earth and Space Science Fellowship Program [80NSSC18K1248]; Heising-Simons FoundationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]