- ID:
- ivo://CDS.VizieR/J/ApJ/848/97
- Title:
- Young stellar variables with KELT for K2. I.
- Short Name:
- J/ApJ/848/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One of the most well-studied young stellar associations, Taurus-Auriga, was observed by the extended Kepler mission, K2, in the spring of 2017. K2 Campaign 13 (C13) is a unique opportunity to study many stars in this young association at high photometric precision and cadence. Using observations from the Kilodegree Extremely Little Telescope (KELT) survey, we identify "dippers," aperiodic and periodic variables among K2 C13 target stars. This release of the KELT data provides the community with long-time baseline observations to assist in the understanding of the more exotic variables in the association. Transient-like phenomena on timescales of months to years are known characteristics in the light curves of young stellar objects, making contextual pre- and post-K2 observations critical to understanding their underlying processes. We are providing a comprehensive set of the KELT light curves for known Taurus-Auriga stars in K2 C13. The combined data sets from K2 and KELT should permit a broad array of investigations related to star formation, stellar variability, and protoplanetary environments.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/878/7
- Title:
- 2yr obs. of JHK variability of stars in Tr37
- Short Name:
- J/ApJ/878/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have monitored nearly a square degree in IC 1396A/Tr 37 over 21 epochs extending over 2014-2016 for sources variable in the JHK bands. In our data, 65%+/-8% of previously identified cluster members show variations, compared with <=0.3% of field stars. We identify 119 members of Tr 37 on the basis of variability, forming an unbiased sample down to the brown dwarf regime. The K-band luminosity function in Tr 37 is similar to that of IC 348 but shifted to somewhat brighter values, implying that the K- and M-type members of Tr 37 are younger than those in IC 348. We introduce methods to classify the causes of variability, based on behavior in the color-color and color-magnitude diagrams. Accretion hot spots cause larger variations at J than at K with substantial scatter in the diagrams; there are at least a dozen, with the most active resembling EXors. Eleven sources are probably dominated by intervention of dust clumps in their circumstellar disks, with color behavior indicating the presence of grains larger than for interstellar dust, presumably due to grain growth in their disks. Thirteen sources have larger variations at K than at J or H. For 11 of them, the temperature fitted to the variable component is very close to 2000K, suggesting that the changes in output are caused by turbulence at the inner rim of the circumstellar disk exposing previously protected populations of grains.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/79
- Title:
- 10yr of GJ176 radial velocities & VR photometry
- Short Name:
- J/ApJ/801/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an in-depth analysis of stellar activity and its effects on radial velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10yr from the High Resolution Spectrograph on the Hobby-Eberly Telescope. These data are supplemented with spectra from previous observations with the HIRES and HARPS spectrographs, and V- and R-band photometry taken over six years at the Dyer and Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth exoplanet in an 8.8-day orbit. However, the velocities of this star are also known to be contaminated by activity, particularly at the 39-day stellar rotation period. We have examined the magnetic activity of GJ 176 using the sodium I D lines, which have been shown to be a sensitive activity tracer in cool stars. In addition to rotational modulation, we see evidence of a long-term trend in our Na I D index, which may be part of a long-period activity cycle. The sodium index is well correlated with our RVs, and we show that this activity trend drives a corresponding slope in RV. Interestingly, the rotation signal remains in phase in photometry, but not in the spectral activity indicators. We interpret this phenomenon as the result of one or more large spot complexes or active regions which dominate the photometric variability, while the spectral indices are driven by the overall magnetic activity across the stellar surface. In light of these results, we discuss the potential for correcting activity signals in the RVs of M dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/132
- Title:
- ~30yr of opt. spectroscopy & Vmag obs. of GW Ori
- Short Name:
- J/ApJ/851/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spatially and spectrally resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the pre-main-sequence hierarchical triple-star system GW Ori. A forward modeling of the ^13^CO and C^18^O J=2-1 transitions permits a measurement of the total stellar mass in this system, 5.29+/-0.09M_{sun}_, and the circumtriple disk inclination, 137.6{deg}+/-2.0{deg}. Optical spectra spanning a 35yr period were used to derive new radial velocities and, coupled with a spectroscopic disentangling technique, revealed that the A and B components of GW Ori form a double-lined spectroscopic binary with a period of 241.50+/-0.05d; a tertiary companion orbits that inner pair with a period of 4218+/-50d. Combining the results from the ALMA data and the optical spectra with three epochs of astrometry in the literature, we constrain the individual stellar masses in the system (M_A_~2.7M_{sun}_, M_B_~1.7M_{sun}_, M_C_~0.9M_{sun}_) and find strong evidence that at least one of the stellar orbital planes (and likely both) is misaligned with the disk plane by as much as 45{deg}. A V-band light curve spanning 30yr reveals several new ~30-day eclipse events 0.1-0.7mag in depth and a 0.2mag sinusoidal oscillation that is clearly phased with the AB-C orbital period. Taken together, these features suggest that the A-B pair may be partially obscured by material in the inner disk as the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude that stellar evolutionary models are consistent with our measurements of the masses and basic photospheric properties if the GW Ori system is ~1Myr old.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/80
- Title:
- 6-yr optical monitoring of the FSRQ 3C 454.3
- Short Name:
- J/ApJ/856/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our photometric monitoring of a flat spectrum radio quasar 3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical color of 3C 454.3 shows an obvious redder-when-brighter trend, which reaches a saturation stage when the source is brighter than 15.15mag at V band. We perform a simulation with multiple values of disk luminosity and spectral index to reproduce the magnitude-color diagram. The results show that the contamination caused by the disk radiation alone is difficult to produce the observed color variability. The variability properties during the outburst in 2009 December are also compared with {gamma}-ray data derived from the Fermi {gamma}-ray space telescope. The flux variation of these two bands follows a linear relation with F_{gamma}_{propto}F_R_^1.14+/-0.07^, which provides observational evidence for the external Compton process in 3C 454.3. Meanwhile, this flux correlation indicates that electron injection is the main mechanism for the variability origin. We also explore the variation of the flux ratio F{gamma}/FR and the detailed structures in the light curves, and discuss some possible origins for the detailed variability behaviors.
- ID:
- ivo://CDS.VizieR/J/ApJS/232/7
- Title:
- 8yr R-band photopolarimetric data of blazar Mrk 421
- Short Name:
- J/ApJS/232/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of 8yr R-band photopolarimetric data of blazar Mrk 421 collected from 2008 February to 2016 May are presented, along with extensive multiwavelength observations covering radio to TeV {gamma}-rays around the flares observed in 2008 May, 2010 March, and 2013 April. The most important results are found in 2013, when the source displayed in the R band a very high brightness state of 11.29+/-0.03mag (93.60+/-1.53mJy) on April 10 and a polarization degree of 11.00%+/-0.44% on May 13. The analysis of the optical data shows that the polarization variability is due to the superposition of two polarized components that might be produced in two distinct emitting regions. An intranight photopolarimetric variability study carried out over seven nights after the 2013 April maximum found flux and polarization variations on the nights of April 14, 15, 16, and 19. In addition, the flux shows a minimum variability timescale of {Delta}t=2.34+/-0.12hr, and the polarization degree presents variations of~1%-2% on a timescale of {Delta}t~minutes. Also, a detailed analysis of the intranight data shows a coherence length of the large-scale magnetic field of l_B_~0.3pc, which is the same order of magnitude as the distance traveled by the relativistic shocks. This result suggests that there is a connection between the intranight polarimetric variations and spatial changes of the magnetic field. Analysis of the complete R-band data along with the historical optical light curve found for this object shows that Mrk 421 varies with a period of 16.26+/-1.78yr.
- ID:
- ivo://CDS.VizieR/J/ApJS/245/18
- Title:
- 9yr R-band photopolarimetric data of 3C 279
- Short Name:
- J/ApJS/245/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An exhaustive analysis of 9yr optical R-band photopolarimetric data of the flat-spectrum radio quasar 3C 279 from 2008 February 27 to 2017 May 25 is presented, along with multiwavelength observing campaigns performed during the flaring activity exhibited in 2009 February/March, 2011 June, 2014 March/April, 2015 June, and 2017 February. In the R band, this source showed the maximum brightness state of 13.68+/-0.11mag (1.36+/-0.20mJy) on 2017 March 2 and the lowest brightness state ever recorded of 18.20+/-0.87 mag (0.16+/-0.03mJy) on 2010 June 17. During the entire period of observations, the polarization degree varied between 0.48%+/-0.17% and 31.65%+/-0.77%, and the electric vector position angle (EVPA) exhibited large rotations between 82.98+/-0.92{deg} and 446.32+/-1.95{deg}. Optical polarization data show that this source has a stable polarized component that varied from~6% (before the 2009 flare) to~13% after the flare. The overall behavior of our polarized variability data supports the scenario of jet precessions as responsible for the observed large rotations of the EVPA. Discrete correlation function analysis shows that the lags between gamma-rays and X-rays compared to the optical R-band fluxes are {Delta}t~31 days and 1 day in 2009. Lags were also found among gamma-rays compared with X-rays and radio of {Delta}t~30 and 43 days in 2011, and among radio and optical R band of {Delta}t~10 days in 2014. A very intense flare in 2017 was observed in optical bands, with a dramatic variation in the polarization degree (from~6% to 20%) in 90 days without exhibiting flaring activity in other wavelengths.
- ID:
- ivo://CDS.VizieR/J/ApJ/837/30
- Title:
- 25yrs monitoring of stellar orbits in the GC
- Short Name:
- J/ApJ/837/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using 25 years of data from uninterrupted monitoring of stellar orbits in the Galactic Center (GC), we present an update of the main results from this unique data set: a measurement of mass and distance to SgrA*. Our progress is not only due to the eight-year increase in time base, but also to the improved definition of the coordinate system. The star S2 continues to yield the best constraints on the mass of and distance to Sgr A*; the statistical errors of 0.13x10^6^M_{sun}_ and 0.12kpc have halved compared to the previous study. The S2 orbit fit is robust and does not need any prior information. Using coordinate system priors, the star S1 also yields tight constraints on mass and distance. For a combined orbit fit, we use 17 stars, which yields our current best estimates for mass and distance: M=4.28+/-0.10|_stat._+/-0.21|_sys_x10^6^M_{sun}_ and R_0_=8.32+/-0.07|_stat._+/-0.14|_sys_kpc. These numbers are in agreement with the recent determination of R_0_ from the statistical cluster parallax. The positions of the mass, of the near-infrared flares from Sgr A*, and of the radio source Sgr A* agree to within 1mas. In total, we have determined orbits for 40 stars so far, a sample which consists of 32 stars with randomly oriented orbits and a thermal eccentricity distribution, plus eight stars that we can explicitly show are members of the clockwise disk of young stars, and which have lower-eccentricity orbits.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/124
- Title:
- 2yrs of eclipse data & precise RVs for LP661-13
- Short Name:
- J/ApJ/836/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of stellar eclipses in the LP 661-13 system. We present the discovery and characterization of this system, including high-resolution spectroscopic radial velocities and a photometric solution spanning two observing seasons. LP 661-13 is a low-mass binary system with an orbital period of 4.7043512_-0.0000010_^+0.0000013^d at a distance of 24.9+/-1.3pc. LP661-13A is a 0.30795+/-0.00084M_{sun}_ star, while LP661-13B is a 0.19400+/-0.00034M_{sun}_ star. The radius of each component is 0.3226+/-0.0033R_{sun}_ and 0.2174+/-0.0023R_{sun}_, respectively. We detect out-of-eclipse modulations at a period slightly shorter than the orbital period, implying that at least one of the components is not rotating synchronously. We find that each component is slightly inflated compared to stellar models, and that this cannot be reconciled through age or metallicity effects. As a nearby eclipsing binary system, where both components are near or below the full-convection limit, LP 661-13 will be a valuable test of models for the structure of cool dwarf stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/10
- Title:
- 12yrs of R-band photometry of the quasar 3C 454.3
- Short Name:
- J/ApJS/253/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present 8523 pairs of R-band optical photometry observations for the quasar 3C 454.3 made during the period of 2006 October - 2018 February on the 70cm meniscus telescope at Abastumani Observatory, Georgia, to study its intraday variabilities (IDVs) and long-term variations, and we have come to the following results. (1) We detected 10 outbursts, a {Delta}R=3.825mag variation, and some IDVs. The IDV timescales are from 4.1 to 285 minutes, with the corresponding variability amplitude being A=2.9%-43.67%. The amplitude increases with IDV timescale. (2) The largest variation over a 1 day timescale is {Delta}R=1.38mag. (3) The IDV timescales suggest that the emission sizes are from 8.9x10^13^cm to 6.20x10^15^cm, and the magnetic field strengths are B=0.18-0.79G. (4) Period analysis results show three possible long-term periods, p=3.04+/-0.02yr, p=1.66+/-0.06yr, and p=1.20+/-0.03yr in the optical light curve. We adopted the accretion disk models and the lighthouse models to period p=3.04+/-0.02yr: in the accretion disk models, the binary black holes have masses M=1.17x10^9^M_{sun}_; in the lighthouse models, we used two boosted jet flux densities to fit the observational light curve. (5) WWZ analysis gives some short-period (high-frequency) signals associated with strong bursts (JD2454302 and JD2454521) with variable frequencies and lasting for the entire observation time span (11.3yr).
