- ID:
- ivo://CDS.VizieR/J/AJ/161/157
- Title:
- 10 years radial-velocity monitoring of Vega with TRES
- Short Name:
- J/AJ/161/157
- Date:
- 18 Jan 2022
- Publisher:
- CDS
- Description:
- We present an analysis of 1524 spectra of Vega spanning 10yr, in which we search for periodic radial-velocity variations. A signal with a periodicity of 0.676day and a semi-amplitude of ~10m/s is consistent with the rotation period measured over much shorter time spans by previous spectroscopic and spectropolarimetric studies, confirming the presence of surface features on this A0 star. The activity signal appears to evolve on long timescales, which may indicate the presence of failed fossil magnetic fields on Vega. TESS data reveal Vega's photometric rotational modulation for the first time, with a total amplitude of only 10ppm. A comparison of the spectroscopic and photometric amplitudes suggests that the surface features may be dominated by bright plages rather than dark spots. For the shortest orbital periods, transit and radial-velocity injection recovery tests exclude the presence of transiting planets larger than 2R{Earth} and most non- transiting giant planets. At long periods, we combine our radial velocities with direct imaging from the literature to produce detection limits for Vegan planets and brown dwarfs out to distances of 15au. Finally, we detect a candidate radial-velocity signal with a period of 2.43days and a semi-amplitude of 6m/s. If caused by an orbiting companion, its minimum mass would be ~20M{Earth}; because of Vega's pole-on orientation, this would correspond to a Jovian planet if the orbit is aligned with the stellar spin. We discuss the prospects for confirmation of this candidate planet.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/877/60
- Title:
- YMGs. I. Young binaries & lithium-rich stars
- Short Name:
- J/ApJ/877/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young stars in the solar neighborhood serve as nearby probes of stellar evolution and represent promising targets to directly image self-luminous giant planets. We have carried out an all-sky search for late-type (~K7-M5) stars within 100pc selected primarily on the basis of activity indicators from the Galaxy Evolution Explorer and ROSAT. Approximately 2000 active and potentially young stars are identified, of which we have followed up over 600 with low-resolution optical spectroscopy and over 1000 with diffraction-limited imaging using Robo-AO at the Palomar 1.5m telescope. Strong lithium is present in 58 stars, implying ages spanning ~10-200Myr. Most of these lithium-rich stars are new or previously known members of young moving groups including TWA, {beta}Pic, Tuc-Hor, Carina, Columba, Argus, ABDor, Upper Centaurus Lupus, and Lower Centaurus Crux; the rest appear to be young low-mass stars without connections to established kinematic groups. Over 200 close binaries are identified down to 0.2"-the vast majority of which are new-and will be valuable for dynamical mass measurements of young stars with continued orbit monitoring in the future.
- ID:
- ivo://CDS.VizieR/J/ApJ/726/18
- Title:
- Young intermediate-mass stars in W5
- Short Name:
- J/ApJ/726/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a survey of young intermediate-mass stars (age<5Myr, 1.5M_{sun}_<M*<=15M_{sun}_) in the W5 massive star-forming region. We use combined optical, near-infrared, and Spitzer Space Telescope photometry and optical spectroscopy to define a sample of stars of spectral types A and B and examine their infrared excess properties. We find objects with infrared excesses characteristic of optically thick disks, i.e., Herbig AeBe stars. These stars are rare: <1.5% of the entire spectroscopic sample of A and B stars, and absent among stars more massive than 2.4M_{sun}_. 7.5% of the A and B stars possess infrared excesses in a variety of morphologies that suggest their disks are in some transitional phase between an initial, optically thick accretion state and later evolutionary states. We identify four morphological classes based on the wavelength dependence of the observed excess emission above theoretical photospheric levels: (1) the optically thick disks; (2) disks with an optically thin excess over the wavelength range 2-24um, similar to that shown by Classical Be stars; (3) disks that are optically thin in their inner regions based on their infrared excess at 2-8um and optically thick in their outer regions based on the magnitude of the observed excess emission at 24um; (4) disks that exhibit empty inner regions (no excess emission at {lambda}<8um) and some measurable excess emission at 24um. A sub-class of disks exhibit no significant excess emission at {lambda}<=5.8um, have excess emission only in the Spitzer 8um band and no detection at 24um. We discuss these spectral energy distribution types, and suggest physical models for disks exhibiting these emission patterns and additional observations to test these theories.
- ID:
- ivo://CDS.VizieR/J/A+AS/139/393
- Title:
- Young Massive Star Clusters. II.
- Short Name:
- J/A+AS/139/393
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 4 lists photometric data for Young Massive Star Clusters identified in a sample of 21 nearby galaxies. The photometric data have been corrected for Galactic foreground extinction. Each cluster is identified by the abbreviated NGC number of its host galaxy and an object number: nxxx-yyy is object number yyy in the galaxy NGC xxx. Effective cluster radii have been obtained by modeling the cluster images as MOFFAT15 functions convolved with the point-spread function measured on the CCD images.
- ID:
- ivo://CDS.VizieR/J/ApJ/695/511
- Title:
- Young massive stars in LHA 120-N 44
- Short Name:
- J/ApJ/695/511
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent site to perform a detailed study of star formation in a mild starburst, as it hosts three regions of star formation at different evolutionary stages, and it is not as complicated and confusing as the 30 Doradus giant HII region. We have obtained Spitzer Space Telescope observations and complementary ground-based 4m uBVIJK observations of N44 to identify candidate massive young stellar objects (YSOs). We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our sample of 60 YSO candidates, ~65% of them are resolved into multiple components or extended sources in high-resolution ground-based images.
- ID:
- ivo://CDS.VizieR/J/ApJ/758/56
- Title:
- Young M dwarfs within 25pc. II. Kinematics
- Short Name:
- J/ApJ/758/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a kinematic study of 165 young M dwarfs with ages of <~300Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of <~25pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (<~3Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and {beta} Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages <~150Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/545
- Title:
- Young stars in Cepheus OB3b
- Short Name:
- J/MNRAS/403/545
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric study of I-band variability in the young association Cepheus OB3b. The study is sensitive to periodic variability on time-scales of less than a day, to more than 20d. After rejection of contaminating objects using V, I, R and narrow-band H{alpha} photometry, we find 475 objects with measured rotation periods, which are very likely pre-main-sequence members of the Cep OB3b star-forming region.
- ID:
- ivo://CDS.VizieR/J/AJ/130/188
- Title:
- Young stars in Trumpler 37 and NGC 7160
- Short Name:
- J/AJ/130/188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of MMT observations of young stars for our study of protoplanetary disks at ages 1-10Myr in two young clusters located in the Cepheus OB2 region: Trumpler 37 (embedded in the HII region IC 1396) and NGC 7160. Using low-resolution optical spectra from the Hectospec multifiber spectrograph, we have tripled the number of known low-mass cluster members, identifying 130 new members in Tr 37 and 30 in NGC 7160. We use indicators of youth (Li absorption at 6707{AA}) and accretion/chromospheric activity (H{alpha} emission) to identify and classify the low-mass cluster members. We derive spectral types for all the low-mass candidates and calculate the individual extinctions and the average over the clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/159/200
- Title:
- Young stellar objects in Lupus star-forming region
- Short Name:
- J/AJ/159/200
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The identification and characterization of stellar members within a star-forming region are critical to many aspects of star formation, including formalization of the initial mass function, circumstellar disk evolution, and star formation history. Previous surveys of the Lupus star-forming region have identified members through infrared excess and accretion signatures. We use machine learning to identify new candidate members of Lupus based on surveys from two space-based observatories: ESA's Gaia and NASA's Spitzer. Astrometric measurements from Gaia's Data Release 2 and astrometric and photometric data from the Infrared Array Camera on the Spitzer Space Telescope, as well as from other surveys, are compiled into a catalog for the random forest (RF) classifier. The RF classifiers are tested to find the best features, membership list, non-membership identification scheme, imputation method, training set class weighting, and method of dealing with class imbalance within the data. We list 27 candidate members of the Lupus star-forming region for spectroscopic follow-up. Most of the candidates lie in Clouds V and VI, where only one confirmed member of Lupus was previously known. These clouds likely represent a slightly older population of star formation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/419/1887
- Title:
- Young stellar objects in NGC 6823
- Short Name:
- J/MNRAS/419/1887
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6823 is a young open cluster that lies at a distance of ~2kpc in the Vulpecula OB1 association. Previous studies using CCD photometry and spectroscopy have identified a Trapezium system of bright O- and B-type stars at its centre, along with several massive O-, B- and A-type stars in the cluster. We present optical VRI and near-infrared JHK photometric observations, complemented with Spitzer/Infrared Array Camera archival data, with an aim to identify the young low-mass population and the disc candidates in this region. Our survey reaches down to I~22mag and K_s_~18mag. There is significant differential reddening within the cluster. We find a bimodal distribution for A_V_, with a peak at ~3mag and a broader peak at ~10mag. We have classified the sources based on the [4.5]-[8] colour, which is least affected by extinction. We find a ~20 per cent fraction of Class I/Class II young stellar objects (YSOs) in the cluster, while a large 80 per cent fraction of the sources have a Class III classification. We have made use of the INT Photometric H{alpha} Survey (IPHAS) in order to probe the strength in H{alpha} emission for this large population of Class III sources. Nearly all of the Class III objects have photospheric (r'-H{alpha}) colours, implying an absence of H{alpha} in emission. This large population of Class III sources is thus likely the extinct field star population rather than the discless YSOs in the cluster. There is a higher concentration of the Class I/II systems in the eastern region of the cluster and close to the central Trapezium. The western part of the cluster mostly contains Class III/field stars and seems devoid of disc sources. We find evidence of a pre-main-sequence population in NGC 6823, in addition to an upper main-sequence population. The pre-main-sequence population mainly consists of young disc sources with ages between ~1 and 5Myr, and at lower masses of ~0.1-0.4M_{sun}_. There may be a possible mass-dependent age spread in the cluster, with the older stars being more massive than the younger ones. The presence of young disc sources in NGC 6823 indicates similar star formation properties in the outer regions of the Galaxy as observed for young clusters in the solar neighbourhood.
