Related papers: Discovery of Dipolar Chromospheres in Two White Dw…
Despite thousands of spectroscopic detections, only four isolated white dwarfs exhibit Balmer emission lines. The temperature inversion mechanism is a puzzle over 30 years old that has defied conventional explanations. One hypothesis is a…
I present the results of a program to spectrophotometrically monitor the L1.5 dwarf 2MASSW J1145572+231730 to identify the cause of photospheric variability in ultra cool dwarfs. Plausible candidates are magnetically-induced star spots and…
We present the JHKs light curves for the double-lined eclipsing binary 2MASS J05352184-0546085, in which both components are brown dwarfs. We analyze these light curves with the published Ic-band light curve and radial velocities to provide…
Aims. The intensity profiles of the C_2 Swan bands in cool DQ white dwarfs cannot be adequately fitted with models that otherwise succesfully reproduce spectral features of the molecule CH in these stars. Initial modelling showed that a…
We present a photometric analysis of 19 DA and 13 DAO white dwarfs (WDs) with effective temperatures exceeding 60 kK, building on the spectral analysis reported in the first paper of this two-part study. By examining archival light curves…
The small DAHe and DAe spectral classes comprise isolated, hydrogen-dominated atmosphere white dwarfs that exhibit variable photometric flux and Balmer line emission. These mysterious systems offer unique insight into the complex interplay…
GD 356 is unique among magnetic white dwarfs because it shows Zeeman-split Balmer lines in pure emission. The lines originate from a region of nearly uniform field strength (delta B/B is approximately 0.1) that covers 10 per cent of the…
We present multi-telescope, ground-based, multiwavelength optical and near-infrared photometry of the variable L3.5 ultra-cool dwarf 2MASSW J0036159+182110. We present 22 nights of photometry of 2MASSW J0036159+182110, including 7 nights of…
GD356 is a magnetic white dwarf (B = 13MG) that uniquely displays weak resolved Zeeman triplets of Halpha and Hbeta in emission. As such, GD356 may be the only known white dwarf with some kind of chromosphere, although accretion from the…
The origin of atmospheric heating in the cool, magnetic white dwarf GD 356 remains unsolved nearly 40 years after its discovery. This once idiosyncratic star with $T_{\rm eff}\approx7500$ K, yet Balmer lines in Zeeman-split emission is now…
Context: There is now growing evidence that some brown dwarfs (BDs) have very strong magnetic fields, and yet their surface temperatures are so low that the coupling is expected to be small between the matter and the magnetic field in the…
Circular polarisation measurements of white dwarfs of various ages and spectral types are useful to understand the origin and evolution of the magnetic field in degenerate stars. In the latest stages of white dwarf evolution, when stars are…
We present a spectro-photometric analysis of 2880 cool white dwarfs within 100 pc of the Sun and cooler than Teff = 10,000 K, with grizy Pan-STARRS photometry and Gaia trigonometric parallaxes available. We also supplement our data sets…
A photometric and spectroscopic analysis of 152 cool white dwarf stars is presented. The discovery of 7 new DA white dwarfs, 2 new DQ white dwarfs, 1 new magnetic white dwarf, and 3 weak magnetic white dwarf candidates, is reported, as well…
Photometric I band light curves of 21 ultra cool M and L dwarfs are presented. Variability with amplitudes of 0.01 to 0.055 magnitudes (RMS) with typical timescales of an hour to several hours are discovered in half of these objects.…
Brown dwarfs and planetary-mass companions display rotationally modulated photometric variability, especially those near the L/T transition. This variability is commonly attributed to top-of-atmosphere (TOA) inhomogeneities, with proposed…
Two recently discovered white dwarfs, WDJ041246.84$+$754942.26 and WDJ165335.21$-$100116.33, exhibit H$\alpha$ and H$\beta$ Balmer line emission similar to stars in the emerging DAHe class, yet intriguingly have not been found to have…
The atmospheres of very cool, hydrogen-rich white dwarfs (Teff <6000 K) are challenging to models because of the increased complexity of the equation of state, chemical equilibrium, and opacity sources in a low-temperature, weakly ionized…
We report on the spectroscopic confirmation of 68 new bright ($G=13.5-17.2$ mag) and blue (pre-)white dwarfs (WDs). This finding has allowed us to almost double the number of the hottest ($T_{\mathrm{eff}} \geq 60$kK) known WDs brighter…
Taking advantage of the Gaia Data Release 2, recent studies have revisited the evolution of carbon-polluted white dwarfs (DQs) across a large range of effective temperatures. These analyses have clearly confirmed the existence of two…