We present results from 1351 high-resolution spectra of 1215 stars in the Orion Nebula Cluster (ONC) and the surrounding Orion 1c association, obtained with the Hectochelle multiobject echelle ...spectrograph on the 6.5 m MMT. We confirmed 1111 stars as members, based on their radial velocity and/or H alpha emission. The radial velocity distribution of members shows a dispersion of image km s super(-1). We found a substantial north-south velocity gradient and spatially coherent structure in the radial velocity distribution, similar to that seen in the molecular gas in the region. We also identified several binary and high velocity stars, a region exhibiting signs of triggered star formation, and a possible foreground population of stars somewhat older than the ONC. Stars without infrared excesses (as detected with the IRAC instrument on the Spitzer Space Telescope) exhibit a wider spread in radial velocity than the infrared excess stars; this spread is mostly due to a blueshifted population of stars that may constitute a foreground population. We also identify some accreting stars, based on H alpha , that do not have detectable infrared excesses with IRAC, and thus are potential transitional disk systems (objects with inner disk holes). We propose that the substructure seen in both the stellar and gaseous components is the result of nonuniform gravitational collapse to a filamentary distribution of gas. The spatial and kinematic correlation between the stellar and gaseous components suggests that the region is very young, probably only image1 crossing time old or less, to avoid shock dissipation and gravitational interactions which would tend to destroy the correlation between stars and gas.
Abstract
We present the early-time light curves of Type Ia supernovae (SNe Ia) observed in the first six sectors of Transiting Exoplanet Survey Satellite (TESS) data. Ten of these SNe were discovered ...by ASAS-SN, seven by ATLAS, six by ZTF, and one by Gaia. For nine of these objects with sufficient dynamic range (>3.0 mag from detection to peak), we fit power-law models and searched for signatures of companion stars. We found a diversity of early-time light-curve shapes, although most of our sources are consistent with fireball models where the flux increases as ∝
t
2
. Three SNe displayed a flatter rise with flux ∝
t
. We did not find any obvious evidence for additional structures, such as multiple power-law components, in the early rising light curves. For assumptions about the SN properties and the observer viewing angle (ejecta mass of 1.4
M
⊙
, expansion velocity of 10
4
km s
−1
, opacity of 0.2 cm
2
g
−1
, and viewing angle of 45°) and a further assumption that any companion stars would be in Roche lobe overflow, it is possible to place upper limits on the radii of any companion stars. Six of the nine SNe had complete coverage of the early-time light curves, and we placed upper limits on the radii of companion stars of ≲32
R
⊙
for these SNe, ≲20
R
⊙
for five of the six, and ≲4
R
⊙
for two of the six. The small sample size did not allow us to put limits on the occurrence rate of companion stars in the progenitors of SNe Ia. However, we expect that TESS observed enough SNe in its two-year primary mission (26 sectors) to either detect the signature of a large companion (
R
> 20
R
⊙
) or constrain the occurrence rate of such systems, at least for the fiducial SN properties adopted here. We also show that TESS is capable of detecting emission from a 1
R
⊙
companion for an SN Ia within 50 Mpc and has a reasonable chance of doing so after about six years.
The Kepler spacecraft is monitoring more than 150,000 stars for evidence of planets transiting those stars. We report the detection of two Saturn-size planets that transit the same Sun-like star, ...based on 7 months of Kepler observations. Their 19.2- and 38.9-day periods are presently increasing and decreasing at respective average rates of 4 and 39 minutes per orbit; in addition, the transit times of the inner body display an alternating variation of smaller amplitude. These signatures are characteristic of gravitational interaction of two planets near a 2:1 orbital resonance. Six radial-velocity observations show that these two planets are the most massive objects orbiting close to the star and substantially improve the estimates of their masses. After removing the signal of the two confirmed giant planets, we identified an additional transiting super-Earth-size planet candidate with a period of 1.6 days.
We report the discovery of the first hot Jupiter in the Hyades open cluster. HD 285507b orbits a V = 10.47 K4.5V dwarf (M sub(*) = 0.734 M sub(middot in circle); R sub(*) = 0.656 R sub(middot in ...circle)) in a slightly eccentric (e = 0.086 super(+0.018) sub(-0.019) ) orbit with a period of 6.0881 super(+0.0019) sub(-0.0018) days. The induced stellar radial velocity corresponds to a minimum companion mass of M sub(p) sin i = 0.917 + or - 0.033 M sub(Jup). Line bisector spans and stellar activity measures show no correlation with orbital phase, and the radial velocity amplitude is independent of wavelength, supporting the conclusion that the variations are caused by a planetary companion. Follow-up photometry indicates with high confidence that the planet does not transit. HD 285507b joins a small but growing list of planets in open clusters, and its existence lends support to a planet formation scenario in which a high stellar space density does not inhibit giant planet formation and migration. We calculate the circularization timescale for HD 285507b to be larger than the age of the Hyades, which may indicate that this planet's non-zero eccentricity is the result of migration via interactions with a third body. We also demonstrate a significant difference between the eccentricity distributions of hot Jupiters that have had time to tidally circularize and those that have not, which we interpret as evidence against Type II migration in the final stages of hot Jupiter formation. Finally, the dependence of the circularization timescale on the planetary tidal quality factor, Q sub(p), allows us to constrain the average value for hot Jupiters to be log Q sub(p) = 6.14 super(+0.41) sub(-0.25).
State of the Field: Extreme Precision Radial Velocities Fischer, Debra A.; Anglada-Escude, Guillem; Arriagada, Pamela ...
Publications of the Astronomical Society of the Pacific,
06/2016, Letnik:
128, Številka:
964
Journal Article
Recenzirano
Odprti dostop
The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm s(-1) measurement ...precision. The presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this bold precision are summarized here. Beginning with the High Accuracy Radial Velocity Planet Searcher spectrograph, technological advances for precision radial velocity (RV) measurements have focused on building extremely stable instruments. To reach still higher precision, future spectrometers will need to improve upon the state of the art, producing even higher fidelity spectra. This should be possible with improved environmental control, greater stability in the illumination of the spectrometer optics, better detectors, more precise wavelength calibration, and broader bandwidth spectra. Key data analysis challenges for the precision RV community include distinguishing center of mass (COM) Keplerian motion from photospheric velocities (time correlated noise) and the proper treatment of telluric contamination. Success here is coupled to the instrument design, but also requires the implementation of robust statistical and modeling techniques. COM velocities produce Doppler shifts that affect every line identically, while photospheric velocities produce line profile asymmetries with wavelength and temporal dependencies that are different from Keplerian signals. Exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. However, higher precision RV measurements are required to serve as a discovery technique for potentially habitable worlds, to confirm and characterize detections from transit missions, and to provide mass measurements for other space-based missions. The future of exoplanet science has very different trajectories depending on the precision that can ultimately be achieved with Doppler measurements.
Using the Hectochelle multifiber spectrograph, we have obtained high-resolution (R ~ 34,000) spectra in the Ha region for a large number of stars in the 4 Myr old cluster Tr 37, containing 146 ...previously known members and 26 newly identified ones. We present the Ha line profiles of all members, compare them to our IR observations of dusty disks (Two Micron All Sky Survey JHK + IRAC + MIPS 24 mm), use the radial velocities as a membership criterion, and calculate the rotational velocities. We find a good correlation between the accretion-broadened profiles and the presence of protoplanetary disks, noting that a small fraction of the accreting stars presents broad profiles with Ha equivalent widths smaller than the canonical limit separating classical T Tauri stars (CTTSs) and weak-lined T Tauri stars (WTTSs). The number of strong accretors appears to be lower than in younger regions, and a large number of CTTSs have very small accretion rates ( <= 10-9 M yr-1). Taking into account that the spectral energy distributions are consistent with dust evolution (grain growth/settling) in the innermost disk, this suggests a parallel evolution of the dusty and gaseous components. We also observe that about half of the 'transition objects' (stars with no IR excesses at l <= 6 mm) do not show any signs of active accretion, whereas the other half is accreting with accretion rates <=10-9 M yr-1. These zero or very low accretion rates reveal important gas evolution and/or gas depletion in the innermost disk, which could be related to grain growth up to planetesimal or even planet sizes. Finally, we examine the rotational velocities of accreting and nonaccreting stars, finding no significant differences that could indicate disk locking at these ages.
Abstract
Studies of close-in planets orbiting M dwarfs have suggested that the M-dwarf radius valley may be well explained by distinct formation timescales between enveloped terrestrials and rocky ...planets that form at late times in a gas-depleted environment. This scenario is at odds with the picture that close-in rocky planets form with a primordial gaseous envelope that is subsequently stripped away by some thermally driven mass-loss process. These two physical scenarios make unique predictions of the rocky/enveloped transition’s dependence on orbital separation such that studying the compositions of planets within the M-dwarf radius valley may be able to establish the dominant physics. Here, we present the discovery of one such keystone planet: the ultra-short-period planet TOI-1634 b (
P
= 0.989 days,
F
=
121
F
⊕
,
r
p
=
1.790
−
0.081
+
0.080
R
⊕
) orbiting a nearby M2 dwarf (
K
s
= 8.7,
R
s
= 0.450
R
⊙
,
M
s
= 0.502
M
⊙
) and whose size and orbital period sit within the M-dwarf radius valley. We confirm the TESS-discovered planet candidate using extensive ground-based follow-up campaigns, including a set of 32 precise radial velocity measurements from HARPS-N. We measure a planetary mass of
4.91
−
0.70
+
0.68
M
⊕
, which makes TOI-1634 b inconsistent with an Earth-like composition at
5.9
σ
and thus requires either an extended gaseous envelope, a large volatile-rich layer, or a rocky composition that is not dominated by iron and silicates to explain its mass and radius. The discovery that the bulk composition of TOI-1634 b is inconsistent with that of Earth supports the gas-depleted formation mechanism to explain the emergence of the radius valley around M dwarfs with
M
s
≲
0.5
M
⊙
.
The Distance to NGC 2264 Baxter, Eric J; Covey, Kevin R; Muench, August A ...
The Astronomical journal,
09/2009, Letnik:
138, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We determine the distance to the open cluster NGC 2264 using a statistical analysis of cluster member inclinations. We derive distance-dependent values of sin i (where i is the inclination angle) for ...97 stars in NGC 2264 from the rotation periods, luminosities, effective temperatures, and projected equatorial rotation velocities, vsin i, measured for these stars. We have measured 96 of the vsin i values in our sample by analyzing high-resolution spectra with a cross-correlation technique. We model the observed distribution of sin i for the cluster by assuming that member stars have random axial orientations and by adopting prescriptions for the measurement errors in our sample. By adjusting the distance assumed in the observed sin i distribution until it matches the modeled distribution, we obtain a best-fit distance for the cluster. We find the data to be consistent with a distance to NGC 2264 of 913 pc. Quantitative tests of our analysis reveal uncertainties of 40 and 110 pc due to sampling and systematic effects, respectively. This distance estimate suggests a revised age for the cluster of ~1.5 Myr, although more detailed investigations of the full cluster membership are required to draw strong conclusions.
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