arXiv subjects

L. Prato

Publications and source records attributed to L. Prato.

At least 37 records · Page 2Linked to original sources

arXiv2018

Orbital Motion of Young Binaries in Ophiuchus and Upper Centaurus-Lupus

We present measurements of the orbital positions and flux ratios of 17 binary and triple systems in the Ophiuchus star forming region and the Upper Centaurus-Lupus cluster based on adaptive optics imaging at the Keck Observatory. We report the detection of visual companions in MML 50 and MML 53 for the first time, as well as the possible detection of a third component in WSB 21. For six systems in our sample, our measurements provide a second orbital position following their initial discoveries over a decade ago. For eight systems with sufficient orbital coverage, we analyze the range of orbital solutions that fit the data. Ultimately, these observations will help provide the groundwork toward measuring precise masses for these pre-main sequence stars and understanding the distribution of orbital parameters in young multiple systems.

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arXiv2017

The Discovery of Herbig-Haro Objects in LDN 673

We report the discovery of twelve faint Herbig-Haro (HH) objects in LDN 673 found using a novel color-composite imaging method that reveals faint Hα emission in complex environments. Follow-up observations in [S II] confirmed their classification as HH objects. Potential driving sources are identified from the Spitzer c2d Legacy Program catalog and other infrared observations. The twelve new HH objects can be divided into three groups: Four are likely associated with a cluster of eight YSO class I/II IR sources that lie between them; five are colinear with the T Tauri multiple star system AS 353, and are likely driven by the same source as HH 32 and HH 332; three are bisected by a very red source that coincides with an infrared dark cloud. We also provide updated coordinates for the three components of HH 332. Inaccurate numbers were given for this object in the discovery paper. The discovery of HH objects and associated driving sources in this region provides new evidence for star formation in the Aquila clouds, implying a much larger T Tauri population in a seldom-studied region.

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arXiv2017

Orbital Solution for the Spectroscopic Binary in the GW Ori Hierarchical Triple

We present the first double-lined orbital solution for the close binary in the GW Ori triple system. Using 12 epochs of infrared spectroscopy, we detected the lines of both stars in the inner pair, previously known as single-lined only. Our preliminary infrared orbital solution has an eccentricity of e = 0.21 +/- 0.10, a period of P = 241.15 +/- 0.72 days, and a mass ratio of q = 0.66 +/- 0.13. We find a larger semi-amplitude for the primary star, K1 = 6.57 +/- 1.00 km s^-1, with an infrared-only solution compared to K1 = 4.41 +/- 0.33 km s^-1 with optical data from the literature, likely the result of line blending and veiling in the optical. The component spectral types correspond to G3 and K0 stars, with vsini values of 43 km s^-1 and 50 km s^-1, respectively. We obtained a flux ratio of alpha = 0.58 +/- 0.14 in the H-band, allowing us to estimate individual masses of 3.2 and 2.7 M_sun for the primary and secondary, respectively, using evolutionary tracks. The tracks also yield a coeval age of 1 Myr for both components to within 1 sigma. GW Ori is surrounded by a circumbinary/circumtriple disk. A tertiary component has been detected in previous studies; however, we did not detect this component in our near-infrared spectra, probably the result of its relative faintness and blending in the absorption lines of these rapidly rotating stars. With these results, GW Ori joins the small number of classical T Tauri, double-lined spectroscopic binaries.

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arXiv2017

The TWA 3 Young Triple System: Orbits, Disks, Evolution

We have characterized the spectroscopic orbit of the TWA 3A binary and provide preliminary families of probable solutions for the TWA 3A visual orbit as well as for the wide TWA 3A--B orbit. TWA 3 is a hierarchical triple located at 34 pc in the $\sim$10 Myr old TW Hya association. The wide component separation is 1."55; the close pair was first identified as a possible binary almost 20 years ago. We initially identified the 35-day period orbital solution using high-resolution infrared spectroscopy which angularly resolved the A and B components. We then refined the preliminary orbit by combining the infrared data with a re-analysis of our high-resolution optical spectroscopy. The orbital period from the combined spectroscopic solution is $\sim$35 days, the eccentricity is $\sim$0.63, and the mass ratio is $\sim$0.84; although this high mass ratio would suggest that optical spectroscopy alone should be sufficient to identify the orbital solution, the presence of the tertiary B component likely introduced confusion in the blended optical spectra. Using millimeter imaging from the literature, we also estimate the inclinations of the stellar orbital planes with respect to the TWA 3A circumbinary disk inclination and find that all three planes are likely misaligned by at least $\sim$30 degrees. The TWA 3A spectroscopic binary components have spectral types of M4.0 and M4.5; TWA 3B is an M3. We speculate that the system formed as a triple, is bound, and that its properties were shaped by dynamical interactions between the inclined orbits and disk.

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arXiv2017

Dynamical Masses of Low Mass Stars in the Taurus and Ophiuchus Star Forming Regions

We report new dynamical masses for 5 pre-main sequence (PMS) stars in the L1495 region of the Taurus star-forming region (SFR) and 6 in the L1688 region of the Ophiuchus SFR. Since these regions have VLBA parallaxes these are absolute measurements of the stars' masses and are independent of their effective temperatures and luminosities. Seven of the stars have masses $<0.6$ solar masses, thus providing data in a mass range with little data, and of these, 6 are measured to precision $< 5 \%$. We find 8 stars with masses in the range 0.09 to 1.1 solar mass that agree well with the current generation of PMS evolutionary models. The ages of the stars we measured in the Taurus SFR are in the range 1-3 MY, and $<1$ MY for those in L1688. We also measured the dynamical masses of 14 stars in the ALMA archival data for Akeson~\&~Jensen's Cycle 0 project on binaries in the Taurus SFR. We find that the masses of 7 of the targets are so large that they cannot be reconciled with reported values of their luminosity and effective temperature. We suggest that these targets are themselves binaries or triples.

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arXiv2016

A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau

The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in its radial velocity (RV) variations measured at infrared (IR) and optical wavelengths. We find that these observations are consistent with a massive planet in a ~9-day period orbit. These results are based on 71 IR RV measurements of this system obtained over 5 years, and on 26 optical RV measurements obtained over 9 years. CI Tau was also observed photometrically in the optical on 34 nights over ~one month in 2012. The optical RV data alone are inadequate to identify an orbital period, likely the result of star spot and activity induced noise for this relatively small dataset. The infrared RV measurements reveal significant periodicity at ~9 days. In addition, the full set of optical and IR RV measurements taken together phase coherently and with equal amplitudes to the ~9 day period. Periodic radial velocity signals can in principle be produced by cool spots, hot spots, and reflection of the stellar spectrum off the inner disk, in addition to resulting from a planetary companion. We have considered each of these and find the planet hypothesis most consistent with the data. The radial velocity amplitude yields an Msin(i) of ~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the circumstellar disk inclination from the literature, we find a planet mass of ~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.

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arXiv2015

Follow-Up Observations of PTFO 8-8695: A 3 MYr Old T-Tauri Star Hosting a Jupiter-mass Planetary Candidate

We present Spitzer 4.5\micron\ light curve observations, Keck NIRSPEC radial velocity observations, and LCOGT optical light curve observations of PTFO~8-8695, which may host a Jupiter-sized planet in a very short orbital period (0.45 days). Previous work by \citet{vaneyken12} and \citet{barnes13} predicts that the stellar rotation axis and the planetary orbital plane should precess with a period of $300 - 600$ days. As a consequence, the observed transits should change shape and depth, disappear, and reappear with the precession. Our observations indicate the long-term presence of the transit events ($>3$ years), and that the transits indeed do change depth, disappear and reappear. The Spitzer observations and the NIRSPEC radial velocity observations (with contemporaneous LCOGT optical light curve data) are consistent with the predicted transit times and depths for the $M_\star = 0.34\ M_\odot$ precession model and demonstrate the disappearance of the transits. An LCOGT optical light curve shows that the transits do reappear approximately 1 year later. The observed transits occur at the times predicted by a straight-forward propagation of the transit ephemeris. The precession model correctly predicts the depth and time of the Spitzer transit and the lack of a transit at the time of the NIRSPEC radial velocity observations. However, the precession model predicts the return of the transits approximately 1 month later than observed by LCOGT. Overall, the data are suggestive that the planetary interpretation of the observed transit events may indeed be correct, but the precession model and data are currently insufficient to confirm firmly the planetary status of PTFO~8-8695b.

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arXiv2015

Radial Velocity Variability of Field Brown Dwarfs

We present paper six of the NIRSPEC Brown Dwarf Spectroscopic Survey, an analysis of multi-epoch, high-resolution (R~20,000) spectra of 25 field dwarf systems (3 late-type M dwarfs, 16 L dwarfs, and 6 T dwarfs) taken with the NIRSPEC infrared spectrograph at the W. M. Keck Observatory. With a radial velocity precision of ~2 km/s, we are sensitive to brown dwarf companions in orbits with periods of a few years or less given a mass ratio of 0.5 or greater. We do not detect any spectroscopic binary brown dwarfs in the sample. Given our target properties, and the frequency and cadence of observations, we use a Monte Carlo simulation to determine the detection probability of our sample. Even with a null detection result, our 1 sigma upper limit for very low mass binary frequency is 18%. Our targets included 7 known, wide brown dwarf binary systems. No significant radial velocity variability was measured in our multi-epoch observations of these systems, even for those pairs for which our data spanned a significant fraction of the orbital period. Specialized techniques are required to reach the high precisions sensitive to motion in orbits of very low-mass systems. For eight objects, including six T dwarfs, we present the first published high-resolution spectra, many with high signal to noise, that will provide valuable comparison data for models of brown dwarf atmospheres.

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arXiv2014

The masses of young stars: CN as a probe of dynamical masses

Aims: We attempt to determine the masses of single or multiple young T Tauri and HAeBe stars from the rotation of their Keplerian disks. Methods:We used the IRAM PdBI interferometer to perform arcsecond resolution images of the CN N=2-1 transition with good spectral resolution. Integrated spectra from the 30-m radiotelescope show that CN is relatively unaffected by contamination from the molecular clouds. Our sample includes 12 sources, among which isolated stars like DM Tau and MWC 480 are used to demonstrate the method and its accuracy. We derive the dynamical mass by fitting a disk model to the emission, a process giving M/D the mass to distance ratio. We also compare the CN results with higher resolution CO data, that are however affected by contamination. Results: All disks are found in nearly perfect Keplerian rotation. We determine accurate masses for 11 stars, in the mass range 0.5 to 1.9 solar masses. The remaining one, DG Tau B, is a deeply embedded object for which CN emission partially arises from the outflow. With previous determination, this leads to 14 (single) stars with dynamical masses. Comparison with evolutionary tracks, in a distance independent modified HR diagram, show good overall agreement (with one exception, CW Tau), and indicate that measurement of effective temperatures are the limiting factor. The lack of low mass stars in the sample does not allow to distinguish between alternate tracks.

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arXiv2014

Orbital Motion in Pre-Main Sequence Binaries

We present results from our ongoing program to map the visual orbits of pre-main sequence binaries in the Taurus star forming region using adaptive optics imaging at the Keck Observatory. We combine our results with measurements reported in the literature to analyze the orbital motion for each binary. We present preliminary orbits for DF Tau, T Tau S, ZZ Tau, and the Pleiades binary HBC 351. Seven additional binaries show curvature in their relative motion. Currently, we can place lower limits on the orbital periods for these systems; full solutions will be possible with more orbital coverage. Five other binaries show motion that is indistinguishable from linear motion. We suspect that these systems are bound and might show curvature with additional measurements in the future. The observations reported herein lay critical groundwork toward the goal of measuring precise masses for low-mass pre-main sequence stars.

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arXiv2014

Refined masses and distance of the young binary Haro 1-14 C

We aim to refine the dynamical masses of the individual component of the low-mass pre-main sequence binary Haro 1-14 C. We combine the data of the preliminary orbit presented previously with new interferometric observations obtained with the four 8m telescopes of the Very Large Telescope Interferometer. The derived masses are $M_a=0.905\pm0.043\,\Msun$ and $M_b=0.308\pm0.011\,\Msun$ for the primary and secondary components, respectively. This is about five times better than the uncertainties of the preliminary orbit. Moreover, the possibility of larger masses is now securely discarded. The new dynamical distance, $d=96\pm\,9\,$pc, is smaller than the distance to the Ophiuchus core with a significance of $2.6\,σ$. Fitting the spectral energy distribution yields apparent diameters of $ϕ_a=0.13\pm0.01\mas$ and $ϕ_b=0.10\pm0.01\mas$ (corresponding to $\Ra=1.50\,\Rsun$ and $\Rb=1.13\,\Rsun$) and a visual extinction of $A_v\approx1.75$. Although the revised orbit has a nearly edge-on geometry, the system is unlikely to be a long-period eclipsing binary. The secondary in Haro~1-14C is one of the few low-mass, pre-main sequence stars with an accurately determined dynamical mass and distance.

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arXiv2013

The quadruple pre-main sequence system LkCa3: Implications for stellar evolution models

We report the discovery that the pre-main sequence object LkCa3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close (~0.5 arc sec) visual pair, with one component being a moderately eccentric 12.94-day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented with new near-infrared spectroscopy shows both visual components to be double-lined, the second one having a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and near-infrared flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we detect also the rotational signal of the primary in the 4.06-day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these constraints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa3 and of the well-known quadruple pre-main sequence system GG Tau with the widely used models from the Lyon series for a mixing length parameter of alpha_ML = 1.0 strongly favor the Dartmouth models.

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arXiv2013

Masses and Distance of the Young Binary NTTS 045251+3016

As part of our continuing campaign to measure the masses of pre-main sequence stars dynamically and thus to assess the reliability of the discrepant theoretical calculations of contraction to the main sequence, we present new results for NTTS 045251+3016, a visual and double-lined spectroscopic binary in the Taurus Star Forming Region. We obtained new high angular resolution astrometry and high spectral resolution spectroscopy at Keck Observatory. The new data lead to a significant revision of previously published orbital parameters. In particular, we find that the masses of the primary and secondary are 0.86+/-0.11 and 0.55+/-0.05 M_sun, respectively, smaller than previously reported, and that the system lies 158.7+/-3.9 pc from the sun, further than previously reported.

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arXiv2013

RX J0513.1+0851 AND RX J0539.9+0956: Two Young, Rapidly Rotating, Spectroscopic Binary Stars

RX J0513.1+0851 and RX J0539.9+0956 were previously identified as young, low-mass, single-lined spectroscopic binary systems and classified as weak-lined T Tauri stars at visible wavelengths. Here we present radial velocities, spectral types, vsini values, and flux ratios for the components in these systems resulting from two-dimensional cross-correlation analysis. These results are based on high-resolution, near-infrared spectroscopy taken with the Keck II telescope to provide a first characterization of these systems as double-lined rather than single-lined. It applies the power of infrared spectroscopy to the detection of cool secondaries; the flux scales as a less steep function of mass in the infrared than in the visible, thus enabling an identification of low-mass secondaries. We found that the RX J0513.1+0851 and RX J0539.9+0956 primary stars are fast rotators, 60 km/s and 80 km/s respectively; this introduces extra difficulty in the detection of the secondary component as a result of the quite broad absorption lines. To date, these are the highest rotational velocities measured for a pre-main sequence spectroscopic binary. The orbital parameters and mass ratios were determined by combining new visible light spectroscopy with our infrared data for both systems. For RX J0513.1+0851, we derived a period of ~4 days and a mass ratio of q = 0.46 +/- 0.01 and for RX J0539.9+0956, a period of ~1117 days and a mass ratio of q = 0.66 +/- 0.01. Based on our derived properties for the stellar components, we estimate the luminosities and hence distances to these binaries at 220 pc and 90 pc. They appear to be significantly closer than previously estimated.

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arXiv2012

A Search for Giant Planet Companions to T Tauri Stars

We present results from an ongoing multiwavelength radial velocity (RV) survey of the Taurus-Auriga star forming region as part of our effort to identify pre--main sequence giant planet hosts. These 1-3 Myr old T Tauri stars present significant challenges to traditional RV surveys. The presence of strong magnetic fields gives rise to large, cool star spots. These spots introduce significant RV jitter which can mimic the velocity modulation from a planet-mass companion. To distinguish between spot-induced and planet-induced RV modulation, we conduct observations at ~6700 Angstroms and ~2.3 microns and measure the wavelength dependence (if any) in the RV amplitude. CSHELL observations of the known exoplanet host Gl 86 demonstrate our ability to detect not only hot Jupiters in the near infrared but also secular trends from more distant companions. Observations of nine very young stars reveal a typical reduction in RV amplitude at the longer wavelengths by a factor of ~2-3. While we can not confirm the presence of planets in this sample, three targets show different periodicities in the two wavelength regions. This suggests different physical mechanisms underlying the optical and K band variability.

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arXiv2012

Discovery of a Very Low Mass Triple with Late-M and T Dwarf Components: LP 704-48/SDSS J0006-0852AB

We report the identification of the M9 dwarf SDSS J000649.16-085246.3 as a spectral binary and radial velocity variable with components straddling the hydrogen burning mass limit. Low-resolution near-infrared spectroscopy reveals spectral features indicative of a T dwarf companion, and spectral template fitting yields component types of M8.5\pm0.5 and T5\pm1. High-resolution near-infrared spectroscopy with Keck/NIRSPEC reveals pronounced radial velocity variations with a semi-amplitude of 8.2\pm0.4 km/s. From these we determine an orbital period of 147.6\pm1.5 days and eccentricity of 0.10\pm0.07, making SDSS J0006-0852AB the third tightest very low mass binary known. This system is also found to have a common proper motion companion, the inactive M7 dwarf LP 704-48, at a projected separation of 820\pm120 AU. The lack of H-alpha emission in both M dwarf components indicates that this system is relatively old, as confirmed by evolutionary model analysis of the tight binary. LP 704-48/SDSS J0006-0852AB is the lowest-mass confirmed triple identified to date, and one of only seven candidate and confirmed triples with total masses below 0.3 Msun currently known. We show that current star and brown dwarf formation models cannot produce triple systems like LP 704-48/SDSS J0006-0852AB, and we rule out Kozai-Lidov perturbations and tidal circularization as a viable mechanism to shrink the inner orbit. The similarities between this system and the recently uncovered low-mass eclipsing triples NLTT 41135AB/41136 and LHS 6343ABC suggest that substellar tertiaries may be common in wide M dwarf pairs.

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arXiv2012

Orbit and Stellar Properties of the Young Triple V807 Tau

We present new orbital measurements of the pre-main sequence triple system, V807 Tau, using adaptive optics imaging at the Keck Observatory. We computed an orbit for the close pair, V807 Tau Ba-Bb, with a period of 12.312 +/- 0.058 years and a semi-major axis of 38.59 +/- 0.16 mas. By modeling the center of mass motion of the components in the close pair relative to the wide component, V807 Tau A, we measured a mass ratio of 0.843 +/- 0.050 for Bb/Ba. Combined with the total mass from the relative orbit, we derived individual masses of M_Ba = 0.564 +/- 0.018 (d/140 pc)^3 Msun and M_Bb = 0.476 +/- 0.017 (d/140 pc)^3 Msun at an average distance of 140 pc to the Taurus star forming region. We computed spectral energy distributions to determine the luminosities of the three components. We also measured their spectral types, effective temperatures, and rotational velocities based on spatially resolved spectra obtained at the Keck Observatory. If the rotational axes are aligned, then the projected rotational velocities imply that V807 Tau Ba and Bb are rotating much faster than V807 Tau A. The uncertainty in the stellar effective temperatures and distance to the system currently limit the comparison of our dynamical mass measurements with predictions based on evolutionary tracks for pre-main sequence stars. We also report preliminary results from a program to map the 3.6 cm radio emission from V807 Tau using the Very Long Baseline Array. With continued monitoring, these observations will provide a precise parallax for placing the dynamical masses on an absolute scale.

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arXiv2012

Dynamical Measurements of the Young Upper Scorpius Triple NTTS 155808-2219

The young, low-mass, triple system NTTS 155808-2219 (ScoPMS 20) was previously identified as a ~17-day period single-lined spectroscopic binary with a tertiary component at 0.21 arcseconds. Using high-resolution infrared spectra, acquired with NIRSPEC on Keck II, both with and without adaptive optics, we measured radial velocities of all three components. Reanalysis of the single-lined visible light observations, made from 1987 to 1993, also yielded radial velocity detections of the three stars. Combining visible light and infrared data to compute the orbital solution produces orbital parameters consistent with the single-lined solution and a mass ratio of q = 0.78 +/- 0.01 for the SB. We discuss the consistency between our results and previously published data on this system, our radial-velocity analysis with both observed and synthetic templates, and the possibility that this system is eclipsing, providing a potential method for the determination of the stars' absolute masses. Over the ~20 year baseline of our observations, we have measured the acceleration of the SB's center-of-mass in its orbit with the tertiary. Long-term, adaptive optics imaging of the tertiary will eventually yield dynamical data useful for component mass estimates.

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