THE NUCLEUS OF THE PLANETARY NEBULA EGB 6 AS A POST-MIRA BINARY

EGB 6 is a faint, large, ancient planetary nebula (PN). Its central star, a hot DAOZ white dwarf (WD), is a prototype of a rare class of PN nuclei associated with dense, compact emission-line knots. The central star also shows excess fluxes in both the near-infrared (NIR) and mid-infrared (MIR). In a 2013 paper, we used Hubble Space Telescope (HST) images to show that the compact nebula is a point-like source, located 0 16 (∼118 AU) from the WD. We attributed the NIR excess to an M dwarf companion star, which appeared to coincide with the dense emission knot. We now present new ground-based NIR spectroscopy, showing that the companion is actually a much cooler source with a continuous spectrum, apparently a dust-enshrouded low-luminosity star. New HST images confirm common proper motion of the emission knot and red source with the WD. The I-band, NIR, and MIR fluxes are variable, possibly on timescales as short as days. We can fit the spectral energy distribution (SED) with four blackbodies (the WD, a ∼1850 K NIR component, and MIR dust at 385 and 175 K). Alternatively, we show that the NIR/MIR SED is very similar to that of Class 0/I young stellar objects. We suggest a scenario in which the EGB 6 nucleus is descended from a wide binary similar to the Mira system, in which a portion of the wind from an AGB star was captured into an accretion disk around a companion star; a remnant of this disk has survived to the present time and is surrounded by gas photoionized by UV radiation from the WD

Terbium-Macrocycle Complexes as Chemical Sensors: Detection of an Aspirin Metabolite in Urine Using a Salicylurate-Specific Receptor Site

Salicylurate (SU) is the major metabolite in urine of acetylsalicylic acid (aspirin) and can be used as a metric to monitor aspirin pharmacokinetics and as an indicator of appendicitis, anemia, and liver disease. Detection in urine and plasma currently requires solvent extraction or other sample handling prior to analysis. We present a simple method to quantify SU in urine via chelation to a terbium binary complex with the macrocycle 1,4,7,10-tetraazacyclododecane-1,7-bisacetate (DO2A). Binding of SU to form the [Tb(DO2A)(SU)]− ternary complex triggers intense luminescence under UV excitation due to an absorbance-energy transfer-emission mechanism. Here we report characterization of the [Tb(DO2A)(SU)]− ternary complex and application of this sensitized lanthanide luminescence method to quantify SU in urine samples following a low-dose aspirin regimen

Near-Infrared Variability of Low Mass Stars in IC 1396A and Tr 37

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.Comment: accepted by Ap