Abstract
Understanding the origin of accretion and dispersal of protoplanetary disks is fundamental for investigating planet formation. Recent numerical simulations show that launching winds are ...unavoidable when disks undergo magnetically driven accretion and/or are exposed to external UV radiation. Observations also hint that disk winds are common. We explore how the resulting wind mass loss rate can be used as a probe of both disk accretion and dispersal. As a proof-of-concept study, we focus on magnetocentrifugal winds, magnetorotational instability turbulence, and external photoevapotaion. By developing a simple yet physically motivated disk model and coupling it with simulation results available in the literature, we compute the wind mass loss rate as a function of external UV flux for each mechanism. We find that different mechanisms lead to different levels of mass loss rate, indicating that the origin of disk accretion and dispersal can be determined, by observing the wind mass loss rate resulting from each mechanism. This determination provides important implications for planet formation. This work thus shows that the ongoing and future observations of the wind mass loss rate for protoplanetary disks are paramount to reliably constrain how protoplanetary disks evolve with time and how planet formation takes place in the disks.
Abstract
Atmospheric escape is a fundamental process that affects the structure, composition, and evolution of many planets. The signatures of escape are detectable on close-in, gaseous exoplanets ...orbiting bright stars, owing to the high levels of extreme-ultraviolet irradiation from their parent stars. The Colorado Ultraviolet Transit Experiment (CUTE) is a CubeSat mission designed to take advantage of the near-ultraviolet stellar brightness distribution to conduct a survey of the extended atmospheres of nearby close-in planets. The CUTE payload is a magnifying near-ultraviolet (2479–3306 Å) spectrograph fed by a rectangular Cassegrain telescope (206 mm × 84 mm); the spectrogram is recorded on a back-illuminated, UV-enhanced CCD. The science payload is integrated into a 6U Blue Canyon Technology XB1 bus. CUTE was launched into a polar, low-Earth orbit on 2021 September 27 and has been conducting this transit spectroscopy survey following an on-orbit commissioning period. This paper presents the mission motivation, development path, and demonstrates the potential for small satellites to conduct this type of science by presenting initial on-orbit science observations. The primary science mission is being conducted in 2022–2023, with a publicly available data archive coming online in 2023.
We report on a study to determine the efficiency of the Large Synoptic Survey Telescope (LSST) to recover the periods, brightnesses, and shapes of RR Lyrae stars' light curves in the volume extending ...to heliocentric distances of 1.5 Mpc. A light curve simulation tool was used to sample the idealized RR Lyrae stars' light curves, returning each as it would have been observed by LSST, including realistic photometric scatter, limiting magnitudes, and telescope downtime. We report here the period, brightness, and light curve shape recovery as a function of apparent magnitude and for survey lengths varying from 1 to 10 years. This study also informs the LSST science operations plan for optimizing observing strategies to achieve particular science goals. We additionally present a new Fe/H-phi sub(31) photometric relation in the r band and a new and generally useful metric for defining period recovery for time domain surveys.
Measuring the temperature and abundance patterns of clouds in the interstellar medium (ISM) provides an observational basis for models of the physical conditions within the clouds, which play an ...important role in studies of star and planet formation. The Colorado High-resolution Echelle Stellar Spectrograph is a far-ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within diffuse molecular and translucent cloud regions. The final two flights of the instrument observed Scorpii (β Sco) and γ Arae. We present flight results of interstellar molecular hydrogen excitation on the sightlines, including measurements of the column densities and temperatures. These results are compared to previous values that were measured using the damping wings of low J″ H absorption features. For β Sco, we find that the derived column density of the J″ = 1 rotational level differs by a factor of 2-3 when compared to the previous observations. We discuss the discrepancies between the two measurements and show that the source of the difference is due to the opacity of higher rotational levels contributing to the J″ = 1 absorption wing, increasing the inferred column density in the previous work. We extend this analysis to 9 Copernicus and 13 Far-Ultraviolet Spectroscopic Explorer spectra to explore the interdependence of the column densities of different rotational levels and how the H kinetic temperature is influenced by these relationships. We find a revised average gas kinetic temperature of the diffuse molecular ISM of T01 = 68 13 K, 12% lower than the value found previously.
We measure H2 temperatures and column densities across the Orion Becklin-Neugebauer/Kleinmann-Low (BN/KL) explosive outflow from a set of 13 near-infrared (IR) H2 rovibrational emission lines ...observed with the TripleSpec spectrograph on Apache Point Observatory's 3.5 m telescope. We find that most of the region is well characterized by a single temperature (∼2000-2500 K), which may be influenced by the limited range of upper-energy levels (6000-20,000 K) probed by our data set. The H2 column density maps indicate that warm H2 comprises 10−5-10−3 of the total H2 column density near the center of the outflow. Combining column density measurements for co-spatial H2 and CO at T = 2500 K, we measure a CO/H2 fractional abundance of 2 × 10−3 and discuss possible reasons why this value is in excess of the canonical 10−4 value, including dust attenuation, incorrect assumptions on co-spatiality of the H2 and CO emission, and chemical processing in an extreme environment. We model the radiative transfer of H2 in this region with ultraviolet (UV) pumping models to look for signatures of H2 fluorescence from H i Ly pumping. Dissociative (J-type) shocks and nebular emission from the foreground Orion H ii region are considered as possible Ly sources. From our radiative transfer models, we predict that signatures of Ly pumping should be detectable in near-IR line ratios given a sufficiently strong source, but such a source is not present in the BN/KL outflow. The data are consistent with shocks as the H2 heating source.
We present the pilot study of the Fluorescent Lyman-Alpha Structures in High-z Environments Survey; the largest integral field spectroscopy survey to date of the circumgalactic medium at z = 2.3-3.1. ...We observed 48 quasar fields with the Palomar Cosmic Web Imager to an average (2 ) limiting surface brightness of 6 × 10−18 erg s−1 cm−2 arcsec−2 (in a 1″ aperture and ∼20 bandwidth). Extended H i Ly emission is discovered around 37/48 of the observed quasars, ranging in projected radius from 14 to 55 proper kiloparsecs (pkpc), with one nebula exceeding 100 pkpc in effective diameter. The dimming-adjusted circularly averaged surface brightness profile peaks at 1 × 10−15 erg s−1 cm−2 arcsec−2 at R ∼ 20 pkpc and integrated luminosities range from 0.4 to 9.4 × 1043 erg s−1. The emission appears to have an eccentric morphology and an average covering factor of ∼30%-40% at small radii. On average, the nebular spectra are redshifted with respect to both the systemic redshift and Ly peak of the quasar spectrum. The integrated spectra of the nebulae mostly have single- or double-peaked profiles with global dispersions ranging from 143 to 708 km s−1, though the individual Gaussian components of lines with complex shapes mostly have dispersions ≤400 km s−1, and the flux-weighted velocity centroids of the lines vary by thousands of km s−1 with respect to the QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with those expected from gravitational motions in dark matter halos of mass Log 10 ( M h M ) 12.2 − 1.2 + 0.7 . We compare these results to existing surveys at higher and lower redshift.
Abstract
We measure H
2
temperatures and column densities across the Orion Becklin-Neugebauer/Kleinmann-Low (BN/KL) explosive outflow from a set of 13 near-infrared (IR) H
2
rovibrational emission ...lines observed with the TripleSpec spectrograph on Apache Point Observatory’s 3.5 m telescope. We find that most of the region is well characterized by a single temperature (∼2000–2500 K), which may be influenced by the limited range of upper-energy levels (6000–20,000 K) probed by our data set. The H
2
column density maps indicate that warm H
2
comprises 10
−5
–10
−3
of the total H
2
column density near the center of the outflow. Combining column density measurements for co-spatial H
2
and CO at
T
= 2500 K, we measure a CO/H
2
fractional abundance of 2 × 10
−3
and discuss possible reasons why this value is in excess of the canonical 10
−4
value, including dust attenuation, incorrect assumptions on co-spatiality of the H
2
and CO emission, and chemical processing in an extreme environment. We model the radiative transfer of H
2
in this region with ultraviolet (UV) pumping models to look for signatures of H
2
fluorescence from H
i
Ly
α
pumping. Dissociative (J-type) shocks and nebular emission from the foreground Orion H
ii
region are considered as possible Ly
α
sources. From our radiative transfer models, we predict that signatures of Ly
α
pumping should be detectable in near-IR line ratios given a sufficiently strong source, but such a source is not present in the BN/KL outflow. The data are consistent with shocks as the H
2
heating source.
Stellar mergers are a brief but common phase in the evolution of binary star systems
. These events have many astrophysical implications; for example, they may lead to the creation of atypical stars ...(such as magnetic stars
, blue stragglers
and rapid rotators
), they play an important part in our interpretation of stellar populations
and they represent formation channels of compact-object mergers
. Although a handful of stellar mergers have been observed directly
, the central remnants of these events were shrouded by an opaque shell of dust and molecules
, making it impossible to observe their final state (for example, as a single merged star or a tighter, surviving binary
). Here we report observations of an unusual, ring-shaped ultraviolet ('blue') nebula and the star at its centre, TYC 2597-735-1. The nebula has two opposing fronts, suggesting a bipolar outflow of material from TYC 2597-735-1. The spectrum of TYC 2597-735-1 and its proximity to the Galactic plane suggest that it is an old star, yet it has abnormally low surface gravity and a detectable long-term luminosity decay, which is uncharacteristic for its evolutionary stage. TYC 2597-735-1 also exhibits Hα emission, radial-velocity variations, enhanced ultraviolet radiation and excess infrared emission-signatures of dusty circumstellar disks
, stellar activity
and accretion
. Combined with stellar evolution models, the observations suggest that TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a look at an unobstructed stellar merger at an evolutionary stage between its dynamic onset and the theorized final equilibrium state, enabling the direct study of the merging process.
Abstract
Ultraviolet spectra of protoplanetary disks trace distributions of warm gas at radii where rocky planets form. We combine Hubble Space Telescope Cosmic Origins Spectrograph observations of H
...2
and CO emission from 12 classical T Tauri stars to more extensively map inner disk surface layers, where gas temperature distributions allow radially stratified fluorescence from the two species. We calculate empirical emitting radii for each species under the assumption that the line widths are entirely set by Keplerian broadening, demonstrating that the CO fluorescence originates further from the stars
r
∼
20
au
than the H
2
r
∼
0.8
au
. This is supported by 2D radiative transfer models, which show that the peak and outer radii of the CO flux distributions generally extend further into the outer disk than the H
2
. These results also indicate that additional sources of Ly
α
photons remain unaccounted for, requiring more complex models to fully reproduce the molecular gas emission. As a first step, we confirm that the morphologies of the UV–CO bands and Ly
α
radiation fields are significantly correlated and discover that both trace the degree of dust disk evolution. The UV tracers appear to follow the same sequence of disk evolution as forbidden line emission from jets and winds, as the observed Ly
α
profiles transition between dominant red wing and dominant blue wing shapes when the high-velocity optical emission disappears. Our results suggest a scenario where UV radiation fields, disk winds and jets, and molecular gas evolve in harmony with the dust disks throughout their lifetimes.
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