We present the discovery of CWISE J050626.96$+$073842.4 (CWISE J0506$+$0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a $(J-K)_{\rm MKO}$ color of 2.97$\pm$0.03 mag and a $J_{\rm MKO}-$W2 color of 4.93$\pm$0.02 mag, making CWISE J0506$+$0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506$+$0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity late-type L/T transition dwarf. The spectrum of CWISE J0506$+$0738 shows possible signatures of CH$_4$ absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8$γ$-T0$γ$. We tentatively find that CWISE J0506$+$0738 is variable at 3-5 $μ$m based on multi-epoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in the $β$ Pic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.
We present the Coordinated Synoptic Investigation of NGC 2264, a continuous 30-day multi-wavelength photometric monitoring campaign on more than 1000 young cluster members using 16 telescopes. The unprecedented combination of multi-wavelength, high-precision, high-cadence, and long-duration data opens a new window into the time domain behavior of young stellar objects. Here we provide an overview of the observations, focusing on results from Spitzer and CoRoT. The highlight of this work is detailed analysis of 162 classical T Tauri stars for which we can probe optical and mid-infrared flux variations to 1% amplitudes and sub-hour timescales. We present a morphological variability census and then use metrics of periodicity, stochasticity, and symmetry to statistically separate the light curves into seven distinct classes, which we suggest represent different physical processes and geometric effects. We provide distributions of the characteristic timescales and amplitudes, and assess the fractional representation within each class. The largest category (>20%) are optical "dippers" having discrete fading events lasting ~1-5 days. The degree of correlation between the optical and infrared light curves is positive but weak; notably, the independently assigned optical and infrared morphology classes tend to be different for the same object. Assessment of flux variation behavior with respect to (circum)stellar properties reveals correlations of variability parameters with H$\alpha$ emission and with effective temperature. Overall, our results point to multiple origins of young star variability, including circumstellar obscuration events, hot spots on the star and/or disk, accretion bursts, and rapid structural changes in the inner disk.
We report the detection of periodic (p = 1.96 hr) bursts of extremely bright, 100% circularly polarized, coherent radio emission from the M9 dwarf TVLM 513-46546. Simultaneous photometric monitoring observations have established this periodicity to be the rotation period of the dwarf. These bursts, which were not present in previous observations of this target, confirm that ultracool dwarfs can generate persistent levels of broadband, coherent radio emission, associated with the presence of kG magnetic fields in a large-scale, stable configuration. Compact sources located at the magnetic polar regions produce highly beamed emission generated by the electron cyclotron maser instability, the same mechanism known to generate planetary coherent radio emission in our solar system. The narrow beams of radiation pass our line of sight as the dwarf rotates, producing the associated periodic bursts. The resulting radio light curves are analogous to the periodic light curves associated with pulsar radio emission highlighting TVLM 513-46546 as the prototype of a new class of transient radio source.
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view Abstract Citations (11) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observational Evidence Linking a Quasar with an Optical Transient Vrba, F. J. ; Luginbuhl, C. B. ; Hartmann, D. H. ; Hudec, R. ; Chaffee, F. H. ; Foltz, C. B. ; Hurley, K. C. Abstract We present evidence for the association of a QSO with a bright optical transient (OT). A V = 20.6 mag QSO with redshift z = 1.78 has been found within the 38" x 62" error ellipse of a bright OT discovered on a Harvard Patrol Camera plate taken in 1905. The chance of finding a random QSO at V <= 20.6 mag within this area is estimated as ~0.5%. Although the OT is within the error circle of the gamma-ray burst (GRB) GB 910219 position determined from the WATCH experiment, the localization for this same event determined from the Third Interplanetary Network does not include the OT or the QSO. Whether the GRB is related to the OT/QSO or not, the probable association of a bright OT with a QSO is a discovery that warrants further investigation. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173872 Bibcode: 1994ApJ...424...68V Keywords: Astronomical Photometry; Astronomical Spectroscopy; Gamma Ray Bursts; Quasars; Surges; Neutron Stars; Radio Bursts; Sky Surveys (Astronomy); Astronomy; GALAXIES: QUASARS: GENERAL full text sources ADS | data products SIMBAD (6) NED (2)
Abstract We have used the UKIRT Hemisphere Survey combined with the UKIDSS Galactic Cluster Survey, the UKIDSS Galactic Plane Survey, and the CatWISE2020 catalog to search for new substellar members of the nearest open cluster to the Sun, the Hyades. Eight new substellar Hyades candidate members were identified and observed with the Gemini/GNIRS near-infrared spectrograph. All eight objects are confirmed as brown dwarfs with spectral types ranging from L6 to T5, with two objects showing signs of spectral binarity and/or variability. A kinematic analysis demonstrates that all eight new discoveries likely belong to the Hyades cluster, with future radial velocity and parallax measurements needed to confirm their membership. CWISE J042356.23+130414.3, with a spectral type of T5, would be the coldest ( T eff ≈ 1100 K) and lowest-mass ( M ≈ 30 M Jup ) free-floating member of the Hyades yet discovered. We further find that high-probability substellar Hyades members from this work and previous studies have redder near-infrared colors than field-age brown dwarfs, potentially due to lower surface gravities and supersolar metallicities.
view Abstract Citations (18) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS OTS 1809+314 and the Gamma-Ray Burst GB 790325b Hartmann, Dieter ; Pogge, Richard W. ; Hurley, Kevin ; Vrba, Frederick J. ; Jennings, Mark C. Abstract Deep CCD images of the field containing the recurring Optical Transient Source (OTS) 1809+314 recently discovered on archival plates of the Sonneberg Observatory are presented. At the position of OTS 1809+314 no optical counterpart brighter than V = 24.0-24.5, r(Gunn) = 22.0-22.5, and I = 22.0-22.5 is found. In the zero proper motion limit our observations place severe constraints on possible quiescent counterparts. There is no compelling evidence to suggest an association between the historical optical transient source and the gamma-ray burst GB 790325b located about 5 arcmin to the east of OTS 1809+314. Publication: The Astrophysical Journal Pub Date: January 1989 DOI: 10.1086/167059 Bibcode: 1989ApJ...336..889H Keywords: Astronomical Photometry; Gamma Ray Bursts; Charge Coupled Devices; Image Analysis; Neutron Stars; Ubv Spectra; Astrophysics; GAMMA RAYS: BURSTS; STARS: VARIABLES full text sources ADS | data products SIMBAD (2)
We use mid-IR (primarily 10 μm) photometry as a diagnostic for the presence of disks with inner cavities among 32 pre–main-sequence stars in Orion and in Taurus-Auriga for which rotation periods are known and for which there is no evidence of inner disks at near-IR wavelengths. Disks with inner cavities are predicted by magnetic disk-locking models that seek to explain the regulation of angular momentum in T Tauri stars. Only three stars in our sample show evidence of excess mid-IR emission. Although these three stars may possess truncated disks consistent with magnetic disk-locking models, the remaining 29 stars in our sample do not. Apparently, stars lacking near-IR excesses in general do not possess truncated disks to which they are magnetically coupled. We discuss the implications of this result for the hypothesis of disk-regulated angular momentum. Evidently, young stars can exist as slow rotators without the aid of present disk locking, and there exist very young stars already rotating at nearly breakup velocity whose subsequent angular momentum evolution will not be regulated by disks. Moreover, we question whether disks, when present, truncate in the manner required by disk-locking scenarios. Finally, we discuss the need for rotational evolution models to take full account of the large dispersion of rotation rates present at 1 Myr; doing so may allow the models to explain the rotational evolution of low-mass pre–main-sequence stars in a way that does not depend on braking by disks.
The dependence of U - B, B - V, and V - I color on V magnitude is examined for ten well-observed T Tauri stars, based on photometry from numerous sources. It is found that the 'color slopes' d(B - V)/dV and d(V - I)/dV, due to variability, differ significantly between stars and tend to be larger for T Tauri stars of later spectral type. Furthermore, when the color slopes are small, the B - V color slope is significantly less than the V - I color slope. All of these results are in accord with the hypothesis that the primary source of large-amplitude brightness variations in T Tauri stars is a changing mix of photospheric regions, hot plage regions, and dark spots on the stellar surface. In addition, the large scatter observed in U - B is consistent with flare-like events.
