[en] We present moderate resolution (R ∼ 3575) optical spectra of 19 known or suspected members of the AB Doradus and β Pictoris Moving Groups, obtained with the DeVeny Spectrograph on the 72 inch Perkins telescope at Lowell Observatory. For four of five recently proposed members, signatures of youth such as Li I 6708 Å absorption and Hα emission further strengthen the case for youth and membership. The lack of detected lithium in the proposed β Pic member TYC 2211-1309-1 implies that it is older than all other K-type members and weakens the case for membership. Effective temperatures are determined via line ratio analyses for the 11 F, G, and early-K stars observed, and via spectral comparisons for the eight late-K and M stars observed. We assemble updated candidate membership lists for these moving groups that account for known binarity. Currently, the AB Dor Moving Group contains 127 proposed members and the β Pic Moving Group holds 77 proposed members. We then use temperature, luminosity, and distance estimates to predict angular diameters for these stars; the motivation is to identify stars that can be spatially resolved with long-baseline optical/infrared interferometers in order to improve age estimates for these groups and to constrain evolutionary models at young ages. Considering the portion of the sky accessible to northern hemisphere facilities (decl. > – 30), six stars have diameters large enough to be spatially resolved (θ > 0.4 mas) with the CHARA Array, which currently has the world's longest baseline of 331 m; this subsample includes the low-mass M2.5 member of AB Dor, GJ 393, which is likely to still be pre-main sequence. For southern hemisphere facilities (decl. < + 30), 18 stars have diameters larger than this limiting size, including the low-mass debris disk star AU Mic (0.72 mas). However, the longest baselines of southern hemisphere interferometers (160 m) are only able to resolve the largest of these, the B6 star α Gru (1.17 mas); proposed long-baseline stations may alleviate the current limitations.

[en] We have conducted a high-dispersion (R ∼ 34,000) optical spectroscopic study of 10 young stars near the cometary globule CG 30 in the Gum Nebula, a diffuse H ii region home to at least 32 cometary globules. All 10 spectroscopically observed stars at the nebula’s northern edge are of low mass (spectral types M4.5–K5), have broad Hα emission, and show spectral veiling. Eight of the 10 are classical T Tauri stars. We spectroscopically measure the photospheric properties of CG 30 IRS 4 inside CG 30. Though embedded, CG 30 IRS 4 is T Tauri–like, with relatively slow projected rotation and moderate veiling. Undepleted Li absorptions, strong Hα emissions, and positions well above the main sequence on an H-R diagram suggest that the 10 stars are ≲1 Myr old. Using our measurements, previous spectroscopy, and previous photometry of 11 other young stars in the area, we determine stellar, kinematic, and accretion properties of a total of 21 young stars. Shared radial velocities, proper motions, distances, and ages suggest that 14 of the young stars (including CG 30 IRS 4) are kinematically related to CG 30. From Gaia DR2 distances to six of these stars, we derive a distance of 358.1 ± 2.2 pc to the cometary globule complex CG 30/31/38. The CG 30 association has an accretor fraction of 29% ± 14%, low for quiescent clusters of similar age but consistent with other irradiated clusters. The Gum Nebula’s moderate radiation environment ($G_0={6.6}_{-<!--\; ???\; -->2.7}^{+3.2}$ at CG 30) may be strong enough to shorten disk lifetimes.

[en] We use the sample of known stars and brown dwarfs within 5 pc of the Sun, supplemented with AFGK stars within 10 pc, to determine which stellar spectral types provide the most habitable real estate—defined as locations where liquid water could be present on Earth-like planets. Stellar temperatures and radii are determined by fitting model spectra to spatially resolved broadband photometric energy distributions for stars in the sample. Using these values, the locations of the habitable zones are calculated using an empirical formula for planetary surface temperature and assuming the condition of liquid water, called here the empirical habitable zone (EHZ). Systems that have dynamically disruptive companions are considered not habitable. We consider companions to be disruptive if the separation ratio of the companion to the habitable zone is less than 5:1. We use the results of these calculations to derive a simple formula for predicting the location of the EHZ for main sequence stars based on V – K color. We consider EHZ widths as more useful measures of the habitable real estate around stars than areas because multiple planets are not expected to orbit stars at identical stellar distances. This EHZ provides a qualitative guide on where to expect the largest population of planets in the habitable zones of main sequence stars. Because of their large numbers and lower frequency of short-period companions, M stars provide more EHZ real estate than other spectral types, possessing 36.5% of the habitable real estate en masse. K stars are second with 21.5%, while A, F, and G stars offer 18.5%, 6.9%, and 16.6%, respectively. Our calculations show that three M dwarfs within 10 pc harbor planets in their EHZs—GJ 581 may have two planets (d with msin i = 6.1 M _⊕; g with msin i = 3.1 M _⊕), GJ 667 C has one (c with msin i = 4.5 M _⊕), and GJ 876 has two (b with msin i = 1.89 M _Jup and c with msin i = 0.56 M _Jup). If Earth-like planets are as common around low-mass stars as recent Kepler results suggest, M stars will harbor more Earth-like planets in habitable zones than any other stellar spectral type

[en] We report the results of an infrared Doppler survey designed to detect brown dwarf and giant planetary companions to a magnitude-limited sample of ultracool dwarfs. Using the NIRSPEC spectrograph on the Keck II telescope, we obtained approximately 600 radial velocity (RV) measurements over a period of six years of a sample of 59 late-M and L dwarfs spanning spectral types M8/L0 to L6. A subsample of 46 of our targets has been observed on three or more epochs. We rely on telluric CH₄ absorption features in Earth's atmosphere as a simultaneous wavelength reference and exploit the rich set of CO absorption features found in the K-band spectra of cool stars and brown dwarfs to measure RVs and projected rotational velocities. For a bright, slowly rotating M dwarf standard we demonstrate an RV precision of 50 m s^-1 and for slowly rotating L dwarfs we achieve a typical RV precision of approximately 200 m s^-1. This precision is sufficient for the detection of close-in giant planetary companions to mid-L dwarfs as well as more equal mass spectroscopic binary systems with small separations (a < 2 AU). We present an orbital solution for the subdwarf binary LSR1610 - 0040 as well as an improved solution for the M/T binary 2M0320 - 04. We compare the distribution of our observed values for the projected rotational velocities, Vsin i, to those in the literature and find that our sample contains examples of slowly rotating mid-L dwarfs, which have not been seen in other surveys. We also combine our RV measurements with distance estimates and proper motions from the literature and estimate the dispersion of the space velocities of the objects in our sample. Using a kinematic age estimate, we conclude that our UCDs have an age of 5.0^+0.7_-0.6 Gyr, similar to that of nearby sun-like stars. We simulate the efficiency with which we detect spectroscopic binaries and find that the rate of tight (a < 1 AU) binaries in our sample is 2.5^+8.6_-1.6%, consistent with recent estimates in the literature of a tight binary fraction of 3%-4%.

[en] Presented are the results of a near-IR photometric survey of 1678 stars in the direction of the ρ Ophiuchus (ρ Oph) star forming region using data from the 2MASS Calibration Database. For each target in this sample, up to 1584 individual J-, H-, and K_s -band photometric measurements with a cadence of ∼1 day are obtained over three observing seasons spanning ∼2.5 yr; it is the most intensive survey of stars in this region to date. This survey identifies 101 variable stars with ΔK_s -band amplitudes from 0.044 to 2.31 mag and Δ(J – K_s ) color amplitudes ranging from 0.053 to 1.47 mag. Of the 72 young ρ Oph star cluster members included in this survey, 79% are variable; in addition, 22 variable stars are identified as candidate members. Based on the temporal behavior of the K_s time-series, the variability is distinguished as either periodic, long time-scale or irregular. This temporal behavior coupled with the behavior of stellar colors is used to assign a dominant variability mechanism. A new period-searching algorithm finds periodic signals in 32 variable stars with periods between 0.49 to 92 days. The chief mechanism driving the periodic variability for 18 stars is rotational modulation of cool starspots while 3 periodically vary due to accretion-induced hot spots. The time-series for six variable stars contains discrete periodic ''eclipse-like'' features with periods ranging from 3 to 8 days. These features may be asymmetries in the circumstellar disk, potentially sustained or driven by a proto-planet at or near the co-rotation radius. Aperiodic, long time-scale variations in stellar flux are identified in the time-series for 31 variable stars with time-scales ranging from 64 to 790 days. The chief mechanism driving long time-scale variability is variable extinction or mass accretion rates. The majority of the variable stars (40) exhibit sporadic, aperiodic variability over no discernable time-scale. No chief variability mechanism could be identified for these variable stars

[en] 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 _* = 0.734 M _☉; R _* = 0.656 R _☉) in a slightly eccentric (e=0.086_−0.019^+0.018) orbit with a period of 6.0881_−0.0018^+0.0019 days. The induced stellar radial velocity corresponds to a minimum companion mass of M _Psin i = 0.917 ± 0.033 M _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 _P, allows us to constrain the average value for hot Jupiters to be logQ_P=6.14_−0.25^+0.41.

[en] We present a multiplexed high-resolution (R ∼ 50,000 median) spectroscopic survey designed to detect exoplanet candidates in two southern star clusters (NGC 2516 and NGC 2422) using the Michigan/Magellan Fiber System (M2FS) on the Magellan/Clay telescope at Las Campanas Observatory. With 128 available fibers in our observing mode, we are able to target every star in the core half-degree of each cluster that could plausibly be a solar-analog member. Our template-based spectral fits provide precise measurements of fundamental stellar properties—T _eff (±30 K), [Fe/H] and [α/Fe] (±0.02 dex), and $v_r\mathrm{s}\mathrm{i}\mathrm{n}(i)$ (±0.3 km s⁻¹)—and radial velocities (RVs) by using telluric absorption features from 7160 to 7290 Å as a wavelength reference for 251 mid-F to mid-K stars (126 in NGC 2516 and 125 in NGC 2422) that comprise our survey. In each cluster, we have obtained ∼10–12 epochs of our targets. Using repeat observations of an RV standard star, we show our approach can attain a single-epoch velocity precision of 25–60 m s⁻¹ over a broad range of signal-to-noise ratios throughout our observational baseline of 1.1 years. Our technique is suitable for nonrapidly rotating stars cooler than mid-F. In this paper, we describe our observational sample and analysis methodology and present a detailed study of the attainable precision and measurement capabilities of our approach. Subsequent papers will provide results for stars observed in the target clusters, analyze our data set of RV time series for stellar jitter and stellar and substellar companions, and consider the implications of our findings on the clusters themselves.

[en] We report the discovery of two giant planets orbiting stars in Praesepe (also known as the Beehive Cluster). These are the first known hot Jupiters in an open cluster and the only planets known to orbit Sun-like, main-sequence stars in a cluster. The planets are detected from Doppler-shifted radial velocities; line bisector spans and activity indices show no correlation with orbital phase, confirming the variations are caused by planetary companions. Pr0201b orbits a V = 10.52 late F dwarf with a period of 4.4264 ± 0.0070 days and has a minimum mass of 0.540 ± 0.039 M_Jup, and Pr0211b orbits a V = 12.06 late G dwarf with a period of 2.1451 ± 0.0012 days and has a minimum mass of 1.844 ± 0.064 M_Jup. The detection of two planets among 53 single members surveyed establishes a lower limit of 3.8^+5.0_–2.4% on the hot Jupiter frequency in this metal-rich open cluster. Given the precisely known age of the cluster, this discovery also demonstrates that, in at least two cases, giant planet migration occurred within 600 Myr after formation. As we endeavor to learn more about the frequency and formation history of planets, environments with well-determined properties—such as open clusters like Praesepe—may provide essential clues to this end.

[en] We present the results of a comprehensive assessment of companions to solar-type stars. A sample of 454 stars, including the Sun, was selected from the Hipparcos catalog with π>40 mas, σ_π/π < 0.05, 0.5 ≤ B - V ≤ 1.0 (∼F6-K3), and constrained by absolute magnitude and color to exclude evolved stars. These criteria are equivalent to selecting all dwarf and subdwarf stars within 25 pc with V-band flux between 0.1 and 10 times that of the Sun, giving us a physical basis for the term 'solar-type'. New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy Array, (2) close companions with speckle interferometry, and (3) wide proper-motion companions identified by blinking multi-epoch archival images. In addition, we include the results from extensive radial-velocity monitoring programs and evaluate companion information from various catalogs covering many different techniques. The results presented here include four new common proper-motion companions discovered by blinking archival images. Additionally, the spectroscopic data searched reveal five new stellar companions. Our synthesis of results from many methods and sources results in a thorough evaluation of stellar and brown dwarf companions to nearby Sun-like stars. The overall observed fractions of single, double, triple, and higher-order systems are 56% ± 2%, 33% ± 2%, 8% ± 1%, and 3% ± 1%, respectively, counting all confirmed stellar and brown dwarf companions. If all candidate, i.e., unconfirmed, companions identified are found to be real, the percentages would change to 54% ± 2%, 34% ± 2%, 9% ± 2%, and 3% ± 1%, respectively. Our completeness analysis indicates that only a few undiscovered companions remain in this well-studied sample, implying that the majority (54% ± 2%) of solar-type stars are single, in contrast to the results of prior multiplicity studies. Our sample is large enough to enable a check of the multiplicity dependence on various physical parameters by analyzing appropriate subsamples. Bluer, more massive stars are seen as more likely to have companions than redder, less massive ones, consistent with the trend seen over the entire spectral range. Systems with larger interaction cross sections, i.e., those with more than two components or long orbital periods, are preferentially younger, suggesting that companions may be stripped over time by dynamical interactions. We confirm the planet-metallicity correlation (i.e., higher metallicity stars are more likely to host planets), but are unable to check it for brown dwarfs due to the paucity of such companions, implying that the brown dwarf desert extends over all separation regimes. We find no correlation between stellar companions and metallicity for B - V < 0.625, but among the redder subset, metal-poor stars ([Fe/H] <-0.3) are more likely to have companions with a 2.4σ significance. The orbital-period distribution of companions is unimodal and roughly log normal with a peak and median of about 300 years. The period-eccentricity relation shows the expected circularization for periods below 12 days, caused by tidal forces over the age of the Galaxy, followed by a roughly flat distribution. The mass-ratio distribution shows a preference for like-mass pairs, which occur more frequently in relatively close pairs. The fraction of planet hosts among single, binary, and multiple systems are statistically indistinguishable, suggesting that planets are as likely to form around single stars as they are around components of binary or multiple systems with sufficiently wide separations. This, along with the preference of long orbital periods among stellar systems, increases the space around stars conducive for planet formation, and perhaps life.

[en] We present a high-precision infrared radial velocity (RV) study of late-type stars using spectra obtained with NIRSPEC at the W. M. Keck Observatory. RV precisions of 50 m s^–1 are achieved for old field mid-M dwarfs using telluric features for wavelength calibration. Using this technique, 20 young stars in the β Pic (age ∼ 12 Myr) and TW Hya (age ∼ 8 Myr) Associations were monitored over several years to search for low-mass companions; we also included the chromospherically active field star GJ 873 (EV Lac) in this survey. Based on comparisons with previous optical observations of these young active stars, RV measurements at infrared wavelengths mitigate the RV noise caused by star spots by a factor of ∼3. Nevertheless, star spot noise is still the dominant source of measurement error for young stars at 2.3 μm, and limits the precision to ∼77 m s^–1 for the slowest rotating stars (v sin i < 6 km s^–1), increasing to ∼168 m s^–1 for rapidly rotating stars (v sin i > 12 km s^–1). The observations reveal both GJ 3305 and TWA 23 to be single-lined spectroscopic binaries; in the case of GJ 3305, the motion is likely caused by its 0.''09 companion, identified after this survey began. The large amplitude, short-timescale variations of TWA 13A are indicative of a hot Jupiter-like companion, but the available data are insufficient to confirm this. We label it as a candidate RV variable. For the remainder of the sample, these observations exclude the presence of any 'hot' (P < 3 days) companions more massive than 8 M_Jup and any 'warm' (P < 30 days) companions more massive than 17 M_Jup, on average. Assuming an edge-on orbit for the edge-on disk system AU Mic, these observations exclude the presence of any hot Jupiters more massive than 1.8 M_Jup or warm Jupiters more massive than 3.9 M_Jup.