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Michael Reefe

Publications and source records attributed to Michael Reefe.

At least 19 recordsLinked to original sources
arXiv2026

Reigniting the FUSE I: Star Formation in Massive Elliptical Galaxies

In this inaugural paper of our "Reigniting the FUSE" series, we present the data collection & reduction, methodology, and preliminary results for a comprehensive and homogeneous reanalysis of all 30 massive elliptical galaxies that have archival far-ultraviolet (FUV) spectra with the Far Ultraviolet Spectroscopic Explorer (FUSE). We perform SED fitting to these spectra, with aperture-matched photometry from GALEX, SDSS, DES/DECaLS, 2MASS, and WISE, and construct a catalogue of high quality constraints on their stellar masses, star formation histories, stellar and gas-phase metallicities, and dust opacities. As a part of this analysis, we have also compiled a comprehensive modern set of stellar template libraries, with high resolution in the FUV, and broad coverage from $90\,\mathring{\rm A}$ - $1000\,{\rm \mu m}$ at lower resolution, which is made available through modified versions of FSPS and Python FSPS. We find strong evidence to suggest that the youngest stars in these systems do not form out of recycled gas from the old stellar populations, but instead are fueled either by gas cooling out of the hot circumgalactic/intracluster medium, or cool gas stripped from nearby or merging dwarf systems. Future papers in this series will reexamine the O VI $\lambda\lambda$1032,1038 $\mathring{\rm A}$ emission in the context of the cooling flow problem.

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arXiv2026

Mapping gas accretion and stellar kinematics to sub-kiloparsec scales in NGC 4696 with JWST/NIRSpec

We present JWST/NIRSpec IFU spectroscopy of the central $618\times618$ pc$^2$ ($\sim3''\times3''$) of NGC 4696, the BCG in the Centaurus cluster. Leveraging the $\sim0.1''$ ($20.6$ pc) pixel size of JWST, we resolve a compact circumnuclear rotating disk (radius of $\sim120$ pc) traced by Pa$\alpha$ and H$_2$ 1$-$0 S(1) emission, which allows a reassessment of the AGN position based on the kinematic centre of this disk. A central Pa$\alpha$ velocity dispersion reaching $\sigma\sim449$ km s$^{-1}$ implies a SMBH mass of $\sim10^9$ M$_\odot$, corresponding to a sphere of influence of $r_\mathrm{inf}\sim60$ pc, resolved by our observations. Position-velocity diagrams reveal an increase from $\sim-200$ to $\sim600$ km s$^{-1}$ on scales of $\sim150$ pc (a gradient of $4.7$ km s$^{-1}$ pc$^{-1}$) and an accretion rate of $\sim18$ M$_\odot$ yr$^{-1}$ feeding the CND. The Pa$\alpha$ emission shows a double-component in the core, with a high-dispersion redshifted component reaching $\sigma\sim600$ km s$^{-1}$. In contrast, MUSE H$\alpha$ observations covering the $\sim10$ kpc-scale filamentary structure recover only weak velocity gradients ($\lesssim150$ km s$^{-1}$) within $\sim300\times300$ pc$^2$ and do not resolve the disk due to larger PSFs and pixel sizes. ALMA CO(2-1) data reveal only compact molecular clumps within a $\sim410\times410$ pc$^2$ region, with no extended counterpart to the structures traced by Pa$\alpha$ and H$_2$ 1$-$0 S(1). Stellar kinematics show a smooth velocity field and broad dispersion profile, clearly decoupled from both the multiphase gas and the hot ICM probed by XRISM. These results provide a direct, spatially resolved view of gas dynamics within the inner few hundred parsecs, demonstrating the power of JWST/NIRSpec to probe SMBH feeding.

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arXiv2026

JWST reveals how black holes are fed: kiloparsec-scale multiphase filaments feed sub-kiloparsec circumnuclear disks

The Centaurus cluster is one of the most important archetypes of radio-mode AGN feedback, with its central galaxy, NGC 4696, launching powerful jets that inflate X-ray cavities and regulate cooling and star formation. NGC 4696 lies within a spectacular multiphase nebula of filaments extending over tens of kiloparsecs and spanning six decades in temperature, from hot (10^8 K) X-ray-emitting plasma to cold molecular gas. Owing to its proximity, Hubble Space Telescope H_alpha imaging reveals a striking S-shaped ionized-gas swirl within the black hole's sphere of influence - the first such structure identified in a cluster core. Here we present the first JWST observations of NGC 4696 with NIRSpec, probing the inner 618 pc * 618 pc at 10 pc resolution. These data reveal that the ionized swirl is a rotating, multiphase circumnuclear disk (CND) physically and kinematically connected to the larger-scale filamentary network. This provides the long-sought missing link between kiloparsec-scale cooling flows and black hole accretion on <100 pc scales. Strikingly, the observed morphology and kinematics are reproduced by tailored magnetohydrodynamic simulations, in which filamentary gas condenses from the hot atmosphere, loses angular momentum, and feeds a rotating CND that mediates accretion onto the black hole. A similar structure in NGC 1275, the Perseus cluster's central galaxy, together with our results on NGC 4696 - two prototypical radio-mode AGN feedback systems - points to a common mechanism: multiphase filaments transport gas from cluster scales down to the vicinity of the black hole via a CND, closing the AGN feedback loop and establishing a physically grounded framework for self-regulated galaxy evolution.

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arXiv2026

BlackHoleWeather -- Jet-regulated chaotic cold accretion across the meso scale: Morphology and thermodynamics

How mechanical AGN feedback couples to multiphase condensation across scales remains a problem in galaxy groups and clusters. It is unclear how jets reshape the chaotic cold accretion (CCA) cycle and regulate black-hole fueling. BlackHoleWeather aims to build a unified description of the AGN baryon cycle across horizon, galactic, and group scales. Here we focus on how weather states shape the morphology and thermodynamics of jet-regulated CCA. We perform two hydrodynamical simulations of a turbulent, radiatively cooling galaxy-group atmosphere with self-regulated AGN feedback. The runs are initialized in two turbulence regimes and evolved with a kinetic mass-loaded jet. The jet prevents cooling via heating, but anisotropically reorganizes condensation through compression, entrainment, and turbulent mixing. In the stronger-turbulence case, condensation starts later but becomes extended, filamentary, and mixed, with a broader hot-warm-cold bridge, a porous cocoon, and burst-dominated fueling. This run evolves toward a cloud-dominated state with inefficient central accretion. In the weaker-turbulence case, condensation starts earlier and remains coherent and centrally confined, yielding a regular cocoon, a longer-lived inner cold reservoir with sustained fueling. In both runs, condensation is suppressed inside the jet channel and survives in the surrounding atmosphere and along the jet-ambient interface. Once condensation begins, SMBH fueling becomes super-Bondi. These results extend CCA from a pure cooling + turbulence problem to a jet-regulated weather process. Ambient turbulence acts as a control parameter, producing an extended stormy phase, a centrally retained rainy cycle, and, in the high-turbulence case, a later cloudy state with inefficient central fueling. The meso scale emerges as the layer linking halo thermodynamics to SMBH feeding within the broader BlackHoleWeather framework.

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arXiv2026

BlackHoleWeather -- Jet-regulated chaotic cold accretion across the meso scale: Variability and kinematics

Chaotic cold accretion (CCA) predicts that supermassive black holes are fed by multiphase clouds condensing from turbulent hot atmospheres. In jet-regulated systems cold gas must also remain dynamically connected to the central accretion region. We investigate how a self-regulated kinetic jet modifies the kinematics, radial transport, and variability of CCA across the meso-scale of a typical galaxy-group atmosphere. The runs differ only in turbulent driving strength. We measure accretion histories, Eddington ratios, power spectra, phase-separated mass fluxes, projected k-plots, and cooling-to-eddy-time (C-ratio) profiles. Both runs become CCA-fed once precipitation begins, with accretion rising from Bondi-like to strongly super-Bondi values while remaining mostly low-Eddington and mechanically dominated. The strongly stirred run develops an early stormy phase with extended condensation, bursty feeding, and strong inflow/outflow variability, but later enters a cloudy phase in which cold and warm gas persist at meso- and inner macro-scales while sink coupling weakens. The calmer run maintains a compact rainy state with a longer-lived central reservoir. Accretion-rate spectra show flicker-like low-frequency slopes and red-noise tails; in the cloudy phase, the normalization drops and the low-frequency slope flattens. Phase-separated fluxes show fountain-like recycling in the strongly stirred run, but inner-kpc recycling in the calmer run. The jet excavates a hot channel where sustained condensation is suppressed, while C~1 is reached mostly outside the cone and near the jet-ambient interface. Jet-regulated CCA is controlled by meso-scale transport, not only by cold-gas production. Within the BlackHoleWeather framework, combined k-plot and C-ratio diagnostics are crucial to distinguish cold gas that is merely present from cold gas dynamically linked to SMBH feeding.

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arXiv2026

A Kiloparsec-Scale Stellar Cavity in the Center of Abell402-BCG May be Caused by Dynamic Interactions with an Ultramassive Black Hole

We present new observations from JWST NIRCam that reveal a striking kpc-wide cavity in the stellar distribution of the central galaxy in the cluster Abell402. Supporting data from HST allow us to rule out extinction due to dust as an explanation and, instead, suggest that this is a localized depression in the stellar density field corresponding to ~2x10^9 Msun in missing stars within a volume of 0.5kpc^3. On larger scales, both the JWST and HST data show evidence for a 2.2kpc flattened core in the stellar distribution (on which the smaller-scale cavity is superimposed), which implies the presence of a central ultra-massive black hole with M_BH = 6 +/- 4 x10^10 Msun. We report evidence for a mid-IR-bright point source at one edge of the cavity, suggesting that this black hole is actively accreting. MUSE spectroscopy reveal that this source is a LINER AGN and that there is a second candidate AGN on the opposite side of the cavity with a relative velocity of 370km/s -- if real, this implies the presence of a kpc-separation dual AGN with a total binary mass of 6 +/- 2 x10^10 Msun, which would make this the most massive binary black hole system discovered to date. We propose that this unique stellar cavity is the result of a short-lived dynamical interaction between at least one supermassive black hole and the background stellar density field, caused either by three-body scattering during binary hardening or the induction of a dipole instability in the stellar density field.

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arXiv2025

An Increase in the Prevalence of Ionized Outflows in Galaxies with Coronal Line Emission: Feedback in Action?

Coronal lines (CLs), which arise from collisionally excited forbidden transitions from highly ionized species, are a powerful diagnostic tool in uncovering active galactic nuclei (AGNs) and constraining their properties. However, recent optical surveys are finding that coronal lines are rarely detected in the majority of local AGNs, possibly as a result of the depletion of elements from the interstellar gas onto dust grains. Prominent CL emission may therefore only arise when dust is being destroyed in the highly ionized gas in AGNs. To explore the possibility that dust destruction may be caused by ionized gas outflows in galaxies with prominent CLs, we present the first large-scale systematic study of ionized outflows, as traced by the [O III] $\lambda$5007 emission, in galaxies displaying CL emission relative to a robust control sample of non-CL-emitting galaxies. We find: 1) galaxies that display CL emission have a significantly elevated outflow incidence rate compared to their matched controls, 2) the outflow luminosity is significantly higher in the CL-emitters, 3) the CL-emitters have systematically lower intrinsic extinction toward the ionized gas compared with the controls, 4) there are significant correlations between the CL luminosity and outflow velocity for the iron CLs, with similar relationships found between the CL FWHM and outflow luminosity. These observations are consistent with dust destruction in an outflowing wind from a dusty torus causing efficient CL emission.

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arXiv2025

Directly Imaging the Cooling Flow in the Phoenix Cluster

In the centers of many galaxy clusters, the hot ($\sim$10$^7$ K) intracluster medium (ICM) can become dense enough that it should cool on short timescales. However, the low measured star formation rates in massive central galaxies and absence of soft X-ray lines from cooling gas suggest that most of this gas never cools - this is known as the "cooling flow problem." The latest observations suggest that black hole jets are maintaining the vast majority of gas at high temperatures. A cooling flow has yet to be fully mapped through all gas phases in any galaxy cluster. Here, we present new observations of the Phoenix cluster using the James Webb Space Telescope to map the [Ne VI] $\lambda$7.652$\mu$m emission line, allowing us to probe gas at 10$^{5.5}$ K on large scales. These data show extended [Ne VI] emission cospatial with (i) the cooling peak in the ICM, (ii) the coolest gas phases, and (iii) sites of active star formation. Taken together, these imply a recent episode of rapid cooling, causing a short-lived spike in the cooling rate which we estimate to be 5,000-23,000 M$_\odot$ yr$^{-1}$. These data provide the first large-scale map of gas at temperatures between 10$^5$-10$^6$ K in a cluster core, and highlight the critical role that black hole feedback plays in not only regulating but also promoting cooling.

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arXiv2025

The CLASS Quasar Catalog: Coronal Line Activity in Type 1 SDSS Quasars

We conduct the first systematic survey of a total of eleven optical coronal lines in the spectra of a large sample of low redshift (z < 0.8) Type 1 quasars observed by the Sloan Digital Sky Survey (SDSS). We find that strong coronal line emission is rare in SDSS even in Type 1 quasars; only 885 out of 19,508 (4.5%) galaxies show at least one coronal line, with higher ionization potential lines ($>100$eV) being even rarer. The [Ne V] $\lambda$3426 line, which constitutes the majority of detections, is strongly correlated with the bolometric luminosity. These findings suggest that the optical coronal lines are significantly suppressed in the majority of local AGNs, possibly as a result of the presence of dust in the emitting regions. We find that the incidence of ionized outflows is significantly higher in coronal line emitters compared with non-coronal line emitters, possibly suggesting that dust destruction in outflows enhances coronal line emission in AGNs. Many coronal lines show line profiles that are broader than those of narrow lines, and are blue-shifted relative the lower ionization potential lines, suggesting outflows in the highly ionized gas. Given the limited number of detections, we do not find any statistically significant trends of detection statistics, or line ratios with black hole mass, Eddington ratio, or AGN bolometric luminosity. The catalog is publicly available and can provide a useful database of the coronal line properties of low redshift quasars that can be compared to the growing number of high-z AGNs discovered by JWST.

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arXiv2025

Cold Gas and Star Formation in the Phoenix Cluster with JWST

We present integral field unit observations of the Phoenix Cluster with the JWST Mid-infrared Instrument's Medium Resolution Spectrometer (MIRI/MRS). We focus this study on the molecular gas, dust, and star formation in the brightest cluster galaxy (BCG). We use precise spectral modeling to produce maps of the silicate dust, molecular gas, and polycyclic aromatic hydrocarbons (PAHs) in the inner $\sim$50 kpc of the cluster. We measure the optical depth from silicates by comparing the observed H$_2$ line ratios to those predicted by excitation models. We provide updated measurements of the total molecular gas mass of $1.9^{+0.5}_{-0.4} \times 10^{10}$ $M_{\odot}$ which agrees with CO-based estimates, providing an estimate of the CO-to-H$_2$ conversion factor of $\alpha_{\rm CO} = 0.8 \pm 0.2\,M_{\odot}\,{\rm pc}^{-2}\,({\rm K}\,{\rm km}\,{\rm s}^{-1})^{-1}$; an updated stellar mass of $M_* = 2.6 \pm 0.5 \times 10^{10}$ $M_\odot$; and star formation rates averaged over 10 and 100 Myr of $\langle{\rm SFR}\rangle_{\rm 10} = 1340 \pm 100$ $M_\odot\,{\rm yr}^{-1}$, and $\langle{\rm SFR}\rangle_{\rm 100} = 740 \pm 80$ $M_\odot\,{\rm yr}^{-1}$, respectively. The H$_2$ emission seems to be powered predominantly by shocks and star formation within the central $\sim 20$ kpc, induced by stellar feedback and radio jets from the active galactic nucleus. Additionally, we find nearly an order of magnitude drop in the star formation rates estimated by PAH fluxes in cool core BCGs compared to field galaxies, suggesting that hot particles from the intracluster medium are destroying PAH grains even in the centralmost 10s of kpc.

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arXiv2023

Giant Outer Transiting Exoplanet Mass (GOT 'EM) Survey: III. Recovery and Confirmation of a Temperate, Mildly Eccentric, Single-Transit Jupiter Orbiting TOI-2010

Large-scale exoplanet surveys like the TESS mission are powerful tools for discovering large numbers of exoplanet candidates. Single-transit events are commonplace within the resulting candidate list due to the unavoidable limitation of observing baseline. These single-transit planets often remain unverified due to their unknown orbital period and consequent difficulty in scheduling follow up observations. In some cases, radial velocity (RV) follow up can constrain the period enough to enable a future targeted transit detection. We present the confirmation of one such planet: TOI-2010 b. Nearly three years of RV coverage determined the period to a level where a broad window search could be undertaken with the Near-Earth Object Surveillance Satellite (NEOSSat), detecting an additional transit. An additional detection in a much later TESS sector solidified our final parameter estimation. We find TOI-2010 b to be a Jovian planet ($M_P = 1.29 \ M_{\rm Jup}$, $R_P = 1.05 \ R_{\rm Jup}$) on a mildly eccentric orbit ($e = 0.21$) with a period of $P = 141.83403$ days. Assuming a simple model with no albedo and perfect heat redistribution, the equilibrium temperature ranges from about 360 K to 450 K from apoastron to periastron. Its wide orbit and bright host star ($V=9.85$) make TOI-2010 b a valuable test-bed for future low-insolation atmospheric analysis.

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arXiv2022

Nuclear Activity in the Low Metallicity Dwarf Galaxy SDSS J0944-0038: A Glimpse into the Primordial Universe

Local low metallicity dwarf galaxies are relics of the early universe and hold clues into the origins of supermassive black holes (SMBHs). In recent work, coronal lines have been used to unveil a population of candidate accreting black holes in dwarf galaxies with gas phase metallicities and stellar masses well below the host galaxies of any previously known AGNs. Using MUSE/VLT observations, we report the detection of [Fe X] $\lambda$6374 coronal line emission and a broad H$\alpha$ line in the nucleus of SDSS J094401.87$-$003832.1, a nearby ($z=0.0049$) metal poor dwarf galaxy almost 500 times less massive than the LMC. The [Fe X] $\lambda$6374 emission is compact and centered on the brightest nuclear source, with a spatial extent of $\approx$100 pc. The [Fe X] luminosity is $\approx 10^{37}$ erg s$^{-1}$, within the range seen in previously identified AGNs in the dwarf galaxy population. This line has never been observed in gas ionized by hot stars. While it can be produced in supernova ejecta, the [Fe X] flux from SDSS J094401.87$-$003832.1 has persisted over the ~19 year time period between the SDSS and MUSE observations, ruling out supernovae as the origin for the emission. The black hole mass measured from the broad H$\alpha$ FWHM and luminosity is $\approx 3150$ M$_\odot$, in line with its stellar mass if virial mass relations and black hole-galaxy scaling relations apply in this mass regime. These observations, together with previously reported multi-wavelength observations, can most plausibly be explained by the presence of an accreting intermediate mass black hole in a primordial galaxy analog. However, we cannot rule out the possibility that current stellar population models of metal poor stars significantly under-predict the stellar ionizing photon flux, and that metal poor stars can produce an extreme ionizing spectrum similar to that produced by AGNs.

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arXiv2022

CLASS Survey Description: Coronal Line Needles in the SDSS Haystack

Coronal lines are a powerful, yet poorly understood, tool to identify and characterize Active Galactic Nuclei (AGNs). There have been few large scale surveys of coronal lines in the general galaxy population in the literature so far. Using a novel pre-selection technique with a flux-to-RMS ratio $F$, followed by Markov-Chain Monte Carlo (MCMC) fitting, we searched for the full suite of 20 coronal lines in the optical spectra of almost 1 million galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 8. We present a catalog of the emission line parameters for the resulting 258 galaxies with detections. The Coronal Line Activity Spectroscopic Survey (CLASS) includes line properties, host galaxy properties, and selection criteria for all galaxies in which at least one line is detected. This comprehensive study reveals that a significant fraction of coronal line activity is missed in past surveys based on a more limited set of coronal lines; $\sim$60% of our sample do not display the more widely surveyed [Fe X] $\lambda$6374. In addition, we discover a strong correlation between coronal line and WISE W2 luminosities, suggesting that the mid-infrared flux can be used to predict coronal line fluxes. For each line we also provide a confidence level that the line is present, generated by a novel neural network, trained on fully simulated data. We find that after training the network to detect individual lines using 100,000 simulated spectra, we achieve an overall true positive rate of 75.49% and a false positive rate of only 3.96%.

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arXiv2022

The TESS Grand Unified Hot Jupiter Survey. II. Twenty New Giant Planets

NASA's Transiting Exoplanet Survey Satellite (TESS) mission promises to improve our understanding of hot Jupiters by providing an all-sky, magnitude-limited sample of transiting hot Jupiters suitable for population studies. Assembling such a sample requires confirming hundreds of planet candidates with additional follow-up observations. Here, we present twenty hot Jupiters that were detected using TESS data and confirmed to be planets through photometric, spectroscopic, and imaging observations coordinated by the TESS Follow-up Observing Program (TFOP). These twenty planets have orbital periods shorter than 7 days and orbit relatively bright FGK stars ($10.9 < G < 13.0$). Most of the planets are comparable in mass to Jupiter, although there are four planets with masses less than that of Saturn. TOI-3976 b, the longest period planet in our sample ($P = 6.6$ days), may be on a moderately eccentric orbit ($e = 0.18\pm0.06$), while observations of the other targets are consistent with them being on circular orbits. We measured the projected stellar obliquity of TOI-1937A b, a hot Jupiter on a 22.4 hour orbit with the Rossiter-McLaughlin effect, finding the planet's orbit to be well-aligned with the stellar spin axis ($|\lambda| = 4.0\pm3.5^\circ$). We also investigated the possibility that TOI-1937 is a member of the NGC 2516 open cluster, but ultimately found the evidence for cluster membership to be ambiguous. These objects are part of a larger effort to build a complete sample of hot Jupiters to be used for future demographic and detailed characterization work.

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arXiv2022

CLASS: Coronal Line Activity Spectroscopic Survey

We conduct the first systematic survey of a comprehensive set of the twenty optical coronal lines in the spectra of nearly 1 million galaxies observed by the Sloan Digital Sky Survey (SDSS) Data Release 8 catalog. This includes often overlooked high ionization-potential (IP) lines such as [Ar X] $\lambda$5533, [S XII] $\lambda$7609, [Fe XI] $\lambda$7892, and [Fe XIV] $\lambda$5303. We find that, given the limited sensitivity of SDSS, strong coronal line emission is extremely rare, with only $\sim 0.03$% of the sample showing at least one coronal line, significantly lower than the fraction of galaxies showing optical narrow line ratios ($\sim 17$%) or mid-infrared colors ($\sim 2$%) indicative of nuclear activity. The coronal line luminosities exhibit a large dynamic range, with values ranging from $\sim10^{34}$ to $10^{42}$ erg s$^{-1}$. We find that a vast majority ($\sim 80$%) of coronal line emitters in dwarf galaxies ($M_* < {9.6} \times 10^9$ M$_\odot$) do not display optical narrow line ratios indicative of nuclear activity, in contrast to higher mass galaxies ($\sim 17$%). Moreover, we find that the highest ionization potential lines are preferentially found in lower mass galaxies. These findings are consistent with the theory that lower mass black holes found in lower mass galaxies produce a hotter accretion disk, which in turn enhances the higher ionization coronal line spectrum. Future coronal line searches with 30 m class telescopes or JWST may provide a pathway into uncovering the intermediate mass black hole population.

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arXiv2022

An asynchronous object-oriented approach to the automation of the 0.8-meter George Mason University campus telescope in Python

We present a unique implementation of Python coding in an asynchronous object-oriented programming (OOP) framework to fully automate the process of collecting data with the George Mason University (GMU) Observatory's 0.8-meter telescope. The goal of this project is to perform automated follow-up observations for the Transiting Exoplanet Survey Satellite (TESS) mission, while still allowing for human control, monitoring, and adjustments. Prior to our implementation, the facility was computer-controlled by a human observer through a combination of webcams, TheSkyX, ASCOM Dome, MaxIm DL, and a weather station. We have automated slews and dome movements, CCD exposures, saving FITS images and metadata, initial focusing, guiding on the target, using the ambient temperature to adjust the focus as the telescope cools through the rest of the night, taking calibration images (darks and flats), and monitoring local weather data. The automated weather monitor periodically checks various weather data from multiple sources to automate the decision to close the observatory during adverse conditions. We have organized the OOP code structure in such a way that each hardware device or important higher-level process is categorized as its own object class or "module" with associated attributes and methods, with inherited common methods across modules for code reusability. To allow actions to be performed simultaneously across different modules, we implemented a multithreaded approach where each module is given its own CPU thread on which to operate concurrently with all other threads. After the initial few modules (camera, telescope, dome, data I/O) were developed, further development of the code was carried out in tandem with testing on sky on clear nights. The code, in its current state, has been tested and used for observations on 171 nights, with more planned usage and feature additions.

astro-ph.IM↗
arXiv2021

Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System

We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic is a young (22 Myr) early M dwarf known to host two transiting planets - $P_{b}\sim8.46$ days, $R_{b}=4.38_{-0.18}^{+0.18}\ R_{\oplus}$, $P_{c}\sim18.86$ days, $R_{c}=3.51_{-0.16}^{+0.16}\ R_{\oplus}$. With visible RVs from CARMENES-VIS, CHIRON, HARPS, HIRES, {\sc {\textsc{Minerva}}}-Australis, and TRES, as well as near-infrared (NIR) RVs from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a $5\sigma$ upper limit to the mass of AU Mic c of $M_{c}\leq20.13\ M_{\oplus}$ and present a refined mass of AU Mic b of $M_{b}=20.12_{-1.57}^{+1.72}\ M_{\oplus}$. Used in our analyses is a new RV modeling toolkit to exploit the wavelength dependence of stellar activity present in our RVs via wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible and near-infrared RVs, we also compute the temporal evolution of RV-``color'' and introduce a regressional method to aid in isolating Keplerian from stellar activity signals when modeling RVs in future works. Using a multi-wavelength Gaussian process model, we demonstrate the ability to recover injected planets at $5\sigma$ significance with semi-amplitudes down to $\approx$ 10\,m\,s$^{-1}$ with a known ephemeris, more than an order of magnitude below the stellar activity amplitude. However, we find that the accuracy of the recovered semi-amplitudes is $\sim$50\% for such signals with our model.

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arXiv2021

Flares, Rotation, and Planets of the AU Mic System from TESS Observations

AU Mic is a young ($\sim$24 Myr), pre-Main Sequence M~dwarf star that was observed in the first month of science observations of the Transiting Exoplanet Survey Satellite (TESS) and re-observed two years later. This target has photometric variability from a variety of sources that is readily apparent in the TESS light curves; spots induce modulation in the light curve, flares are present throughout (manifesting as sharp rises with slow exponential decay phases), and transits of AU Mic b may be seen by eye as dips in the light curve. We present a combined analysis of both TESS Sector 1 and Sector 27 AU Mic light curves including the new 20-second cadence data from TESS Year 3. We compare flare rates between both observations and analyze the spot evolution, showing that the activity levels increase slightly from Sector 1 to Sector 27. Furthermore, the 20-second data collection allows us to detect more flares, smaller flares, and better resolve flare morphology in white light as compared to the 2-minute data collection mode. We also refine the parameters for AU Mic b by fitting three additional transits of AU Mic b from Sector 27 using a model that includes stellar activity. We show that the transits exhibit clear transit timing variations (TTVs) with an amplitude of $\sim$80 seconds. We also detect three transits of a 2.8 $R_\oplus$ planet, AU Mic c, which has a period of 18.86 days.

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