58 research outputs found
tofflemire/saphires: Zenodo archive
No full textThis is a re-release of v0.1.10 that enables a Zenodo DOI link.</p
Pulsed Accretion in the T Tauri Binary TWA 3A
No full textTWA 3A is the most recent addition to a small group of young binary systems that both actively accrete from a circumbinary disk and have spectroscopic orbital solutions. As such, it provides a unique opportunity to test binary accretion theory in a well-constrained setting. To examine TWA 3A's time-variable accretion behavior, we have conducted a two-year, optical photometric monitoring campaign, obtaining dense orbital phase coverage (similar to 20 observations per orbit) for similar to 15 orbital periods. From U-band measurements we derive the time-dependent binary mass accretion rate, finding bursts of accretion near each periastron passage. On average, these enhanced accretion events evolve over orbital phases 0.85 to 1.05, reaching their peak at periastron. The specific accretion rate increases above the quiescent value by a factor of similar to 4 on average but the peak can be as high as an order of magnitude in a given orbit. The phase dependence and amplitude of TWA 3A accretion is in good agreement with numerical simulations of binary accretion with similar orbital parameters. In these simulations, periastron accretion bursts are fueled by periodic streams of material from the circumbinary disk that are driven by the binary orbit. We find that TWA 3A's average accretion behavior is remarkably similar to DQ Tau, another T Tauri binary with similar orbital parameters, but with significantly less variability from orbit to orbit. This is only the second clear case of orbital-phase-dependent accretion in a T Tauri binary.Sigma Xi Honors Society; University of Wisconsin-Madison Graduate SchoolSCI(E)ARTICLE284
Probing the flare atmospheres of M dwarfs using infrared emission lines
No full textWe present the results of a campaign to monitor active M dwarfs using infrared spectroscopy, supplemented with optical photometry and spectroscopy. We detected 16 flares during nearly 50 hr of observations on EV Lac, AD Leo, YZ CMi, and VB 8. The three most energetic flares also showed infrared emission, including the first reported detections of P\u3b2, P\u3b3, He I \u3bb10830, and Br\u3b3 during an M dwarf flare. The strongest flare (\u394u = 4.02 on EV Lac) showed emission from H\u3b3, H\u3b4, He I \u3bb4471, and Ca II K in the UV/blue and P\u3b2, P\u3b3, P\u3b4, Br\u3b3, and He I \u3bb10830 in the infrared. The weaker flares (\u394u = 1.68 on EV Lac and \u394U = 1.38 on YZ CMi) were only observed with photometry and infrared spectroscopy; both showed emission from P\u3b2, P\u3b3, and He I \u3bb10830. The strongest infrared emission line, P\u3b2, occurred in the active mid-M dwarfs with a duty cycle of 3%-4%. To examine the most energetic flare, we used the static NLTE radiative transfer code RH to produce model spectra based on a suite of one-dimensional model atmospheres. Using a hotter chromosphere than previous one-dimensional atmospheric models, we obtain line ratios that match most of the observed emission lines.Peer reviewed: YesNRC publication: Ye
Upper Limits on Stellar Companions to the Kepler-34 and Kepler-35 Systems
No full textWe obtained new spectra of Kepler-34 and Kepler-35 with Keck-HIRES—nearly a decade after these systems were originally characterized with this spectrograph and other instruments—to search for radial velocity (RV) trends from a potential third stellar-mass companion at long periods. For Kepler-34, we rule out coplanar stellar masses as low as 0.12 M _⊙ at an orbital period of ≲52 yr. For Kepler-35, we rule out stellar masses of 0.13 M _⊙ at orbital periods of ≲55 yr. Highly stable, extreme precision RV instruments, as well as improved methodologies in characterizing double-lined spectroscopic binaries that come with these new instruments, will provide an opportunity to push these mass limits lower in the future
The Helium 10830 Å line in young stars: stellar activity and implications for exosphere detection
No full textThe evolutionary pathway of small rocky planet atmospheres, which dictates habitability, is ill-constrained. Planets lose atmosphere over time, but the driver is unclear (e.g. photoevaporation, contraction heat). The cause of this atmospheric sculpting affects the type of atmosphere that is retained and the potential desiccation of the planetary surface from UV irradiation. Observing planetary atmospheres over time, especially in youth when mass loss is most dynamic, can constrain the evolutionary mechanisms. Such a study requires confirmation of evaporating atmospheres, or exospheres, by detecting the planetary mass loss via transit spectroscopy. However, stellar activity causes temporally coherent noise across the spectrum that can manifest as changes in the spectral line strength and prevent the detection of an exosphere. This includes the Helium 10830 A infrared triplet, which is an increasingly popular probe of atmospheric loss. The Helium feature is intrinsically variable in M-dwarfs, but its variability is not known in other types of stars, particularly at young ages when both stellar activity and planetary mass loss are greatest. We present years-long spectral time series from the Habitable-zone Planet Finder (HPF) of 10 young transiting planet hosts (ages of 20 Myr to 1 Gyr) to measure the amplitude and timescale of young stellar He variability. The long-term variability in the He triplet is large enough to impede exosphere detection at the youngest ages, but approaches the field level above roughly 500 Myr. We use the relationship between the typical He line profiles and stellar properties to extract information of the nature of the stellar He feature. These results show that accurate, contemporaneous models of the out-of-transit line profile are needed to precisely measure excess absorption at young ages
Accretion and Magnetic Reconnection in the Classical T Tauri Binary DQ Tau
No full textThe theory of binary star formation predicts that close binaries ( a < 100 au) will experience periodic pulsed accretion events as streams of material form at the inner edge of a circumbinary disk (CBD), cross a dynamically cleared gap, and feed circumstellar disks or accrete directly onto the stars. The archetype for the pulsed accretion theory is the eccentric, short-period, classical T Tauri binary DQ Tau. Low-cadence (∼daily) broadband photometry has shown brightening events near most periastron passages, just as numerical simulations would predict for an eccentric binary. Magnetic reconnection events (flares) during the collision of stellar magnetospheres near periastron could, however, produce the same periodic, broadband behavior when observed at a one-day cadence. To reveal the dominant physical mechanism seen in DQ Tau’s low-cadence observations, we have obtained continuous, moderate-cadence, multiband photometry over 10 orbital periods, supplemented with 27 nights of minute-cadence photometry centered on four separate periastron passages. While both accretion and stellar flares are present, the dominant timescale and morphology of brightening events are characteristic of accretion. On average, the mass accretion rate increases by a factor of five near periastron, in good agreement with recent models. Large variability is observed in the morphology and amplitude of accretion events from orbit to orbit. We argue that this is due to the absence of stable circumstellar disks around each star, compounded by inhomogeneities at the inner edge of the CBD and within the accretion streams themselves. Quasiperiodic apastron accretion events are also observed, which are not predicted by binary accretion theory
THE IMPLICATIONS OF M DWARF FLARES ON THE DETECTION AND CHARACTERIZATION OF EXOPLANETS AT INFRARED WAVELENGTHS
No full textA search for stellar siblings of the ~ 200 Myr TOI-251b planetary system
No full textYoung planets (< 1 Gyr) are helpful for studying the physical processes
occurring at the early stage of planet evolution. TOI-251 b is a recently
discovered sub-Neptune orbiting a young G dwarf, which has an imprecise age
estimation of 40-320 Myr. We select TOI-251 sibling candidates based on
kinematics and spatial proximity to TOI-251, and further use the
color-magnitude diagram (CMD) to refine the list and to compare to multiple
open clusters. We report stellar rotational period for 321 sibling candidates
in a 50 pc radius around TOI-251 by analyzing their stellar light curves, and
find a color - rotational period sequence that lie in between the Group X (300
Myr) and Pleiades (120 Myr) members, suggesting an age ~ 200 Myr. A
quantitative age analysis by using gyrochronology relations give 204 45
Myr, consistent with the average Li-age of selected siblings (238 38 Myr)
and the Gaia variability age (193 Myr). The detection fraction of
comoving candidates that have short rotational period is 68.1%, much higher
than the typical value in the field (14% - 16% from Kepler). The overdensity of
young stars and consistency in age of stellar siblings suggest a potential
young association candidate in the Pheonix-Grus constellation. Though TOI-251 b
has a radius larger than most of its field-age counterparts, we are uncertain
whether TOI-251 is inflated due to a lack of knowledge on the planet's mass.Comment: 19 pages, 9 figures, 3 tables, ApJ accepte
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