Search

We report here the results obtained from a systematic optical photometric survey aimed at finding new compact binary millisecond pulsars (also known as "spiders"): the COmpact BInary PULsar SEarch (COBIPULSE). We acquired multi-band optical images over one year around $33$ unidentified Fermi-LAT sources, selected as pulsar candidates based on their curved GeV spectra and steady $\gamma$-ray emission. We present the discovery of four optical variables coinciding with the Fermi sources 3FGL J0737.2$-$3233, 3FGL J2117.6$+$3725 (two systems in this field) and 3FGL J2221.6$+$6507, which we propose as new candidate spider systems. Indeed, they all show optical flux modulation consistent with orbital periods of $0.3548(5) \ \mathrm{d}$, $0.25328(6) \ \mathrm{d}$, $0.441961(2) \ \mathrm{d}$, and $0.165(4) \ \mathrm{d}$, respectively, with amplitudes $\gtrsim 0.3 \ \mathrm{mag}$ and colors compatible with companion star temperatures of $5000$--$6000 \ \mathrm{K}$. These properties are consistent with the "redback" sub-class of spider pulsars. If confirmed as a millisecond pulsar, 3FGL J0737.2$-$3233 will be the closest known spider to Earth ($D=659_{-20}^{+16} \ \mathrm{pc}$, from Gaia-DR3 parallax). We searched and did not find any X-ray sources matching our four candidates, placing $3\sigma$ upper limits of $\sim10^{31}$--$10^{32} \ \mathrm{erg} \ \mathrm{s}^{-1}$ ($0.3$--$10 \ \mathrm{keV}$) on their soft X-ray luminosities. We also present and discuss other multi-wavelength information on our spider candidates, from infrared to X-rays., Comment: 38 pages, 93 figures, 4 tables. This paper has been accepted for publication in ApJ

A comprehensive multi-wavelength campaign has been carried out to probe stellar activity and variability in the young Sun-like star $\iota$-Horologii. We present the results from long-term spectropolarimetric monitoring of the system by using the ultra-stable spectropolarimeter/velocimeter HARPS at the ESO 3.6-m telescope. Additionally, we included high-precision photometry from the NASA Transiting Exoplanet Survey Satellite (TESS) and observations in the far- and near-ultraviolet spectral regions using the STIS instrument on the NASA/ESA Hubble Space Telescope (HST). The high-quality dataset allows a robust characterisation of the star's rotation period, as well as a probe of the variability using a range of spectroscopic and photometric activity proxies. By analyzing the gradient of the power spectra (GPS) of the TESS lightcurves we constrained the faculae-to-spot driver ratio ($\rm S_{fac}/S_{spot}$) to 0.510$\pm$0.023, which indicates that the stellar surface is spot dominated during the time of the observations. We compared the photospheric activity properties derived from the GPS method with a magnetic field map of the star derived using Zeeman-Doppler imaging (ZDI) from simultaneous spectropolarimetric data for the first time. Different stellar activity proxies enable a more complete interpretation of the observed variability. For example, we observed enhanced emission in the HST transition line diagnostics C IV and C III, suggesting a flaring event. From the analysis of TESS data acquired simultaneously with the HST data, we investigate the photometric variability at the precise moment that the emission increased and derive correlations between different observables, probing the star from its photosphere to its corona.

Recent atmospheric models for brown dwarfs suggest that the existence of clouds in substellar objects is not needed to reproduce their spectra, nor their rotationally-induced photometric variability, believed to be due to the heterogeneous cloud coverage of brown dwarf atmospheres. Cloud-free atmospheric models also predict that their flux should not be polarized, as polarization is produced by the light-scattering of particles in the inhomogeneous cloud layers of brown dwarf atmospheres. To shed light on this dichotomy, we monitored the linear polarization and photometric variability of the most variable brown dwarf, 2MASS J21392676+0220226. We used FORS2 at the UT1 telescope to monitor the object in the z-band for six hours, split on two consecutive nights, covering one-third of its rotation period. We obtained the Stokes parameters, and we derived its time-resolved linear polarization, for which we did not find significant linear polarization (P = 0.14+\-0.07 %). We modeled the linear polarimetric signal expected assuming a map with one or two spot-like features and two bands using a polarization-enabled radiative-transfer code. We obtained values compatible with the time-resolved polarimetry obtained for 2MASS J21392676+0220226. The lack of significant polarization might be due to photometric variability produced mostly by banded structures or small-scale vortices, which cancel out the polarimetric signal from different regions of the dwarf's disk. Alternatively, the lack of clouds in 2MASS J21392676+0220226 would also explain the lack of polarization. Further linear polarimetric monitoring of 2MASS J21392676+0220226, during at least one full rotational period, would help to confirm or discard the existence of clouds in its atmosphere., Comment: Accepted for publication Feb 28

We use 1-m class telescopes and the Transiting Exoplanet Survey Satellite (TESS) to explore the photometric variability of all known rapidly rotating ($v\sin{i}\gtrsim30$ km\,s$^{-1}$) ultra-cool ($\geq$M7) dwarfs brighter than $I\approx17.5$ mag. For a sample of 13 M7--L1.5 dwarfs without prior photometric periods, we obtained $I$-band light curves with the SMARTS 1.3m and WIYN 0.9m telescopes and detected rotation-modulated photometric variability in three of them. Seven of our targets were also observed by TESS and six of them show significant periodicities compatible with the estimated rotation periods of the targets. We investigate the potential of TESS to search for rotation-modulated photometric variability in ultra-cool dwarfs and find that its long stare enables $<$80~h periodic variations to be retrieved with $\leq$1\% amplitudes for ultra-cool dwarfs up to a TESS magnitude of 16.5. We combine these results with the periods of all other known photometrically-periodic ultra-cool dwarfs from the literature, and find that the periods of ultra-cool dwarfs range between 1 and 24 h, although the upper limit is likely an observational bias. We also observe that the minimum rotation periods follow a lower envelope that runs from $\approx$2 h at spectral type $\approx$M8 to $\approx$1 h at spectral type T., Comment: Accepted for publication in MNRAS

In the JWST, Extremely Large Telescopes, and LUVOIR era, we expect to characterize a number of potentially habitable Earth-like exoplanets. However, the characterization of these worlds depends crucially on the accuracy of theoretical models. Validating these models against observations of planets with known properties will be key for the future characterization of terrestrial exoplanets. Due to its sensitivity to the micro- and macro-physical properties of an atmosphere, polarimetry will be an important tool that, in tandem with traditional flux-only observations, will enhance the capabilities of characterizing Earth-like planets. In this paper we benchmark two different polarization-enabled radiative-transfer codes against each other and against unique linear spectropolarimetric observations of the earthshine that cover wavelengths from $\sim$0.4 to $\sim$2.3 $\mu$m. We find that while the results from the two codes generally agree with each other, there is a phase dependency between the compared models. Additionally, with our current assumptions, the models from both codes underestimate the level of polarization of the earthshine. We also report an interesting discrepancy between our models and the observed 1.27 $\mu$m $O_2$ feature in the earthshine, and provide an analysis of potential methods for matching this feature. Our results suggest that only having access to the 1.27 $\mu$m $O_2$ feature coupled with a lack of observations of the $O_2$ A and B bands could result in a mischaracterization of an Earth-like atmosphere. Providing these assessments is vital to aid the community in the search for life beyond the solar system., Comment: 24 pages, 18 figures

We report the discovery and characterization of the transiting extrasolar planet TOI-1710$\:$b. It was first identified as a promising candidate by the Transiting Exoplanet Survey Satellite (TESS). Its planetary nature was then established with SOPHIE and HARPS-N spectroscopic observations via the radial-velocity method. The stellar parameters for the host star are derived from the spectra and a joint Markov chain Monte-Carlo (MCMC) adjustment of the spectral energy distribution and evolutionary tracks of TOI-1710. A joint MCMC analysis of the TESS light curve and the radial-velocity evolution allows us to determine the planetary system properties. From our analysis, TOI-1710$\:$b is found to be a massive warm super-Neptune ($M_{\rm p}=28.3\:\pm\:4.7\:{\rm M}_{\rm Earth}$ and $R_{\rm p}=5.34\:\pm\:0.11\:{\rm R}_{\rm Earth}$) orbiting a G5V dwarf star ($T_{\rm eff}=5665\pm~55\mathrm{K}$) on a nearly circular 24.3-day orbit ($e=0.16\:\pm\:0.08$). The orbital period of this planet is close to the estimated rotation period of its host star $P_{\rm rot}=22.5\pm2.0~\mathrm{days}$ and it has a low Keplerian semi-amplitude $K=6.4\pm1.0~\mathrm{m\:s^{-1}}$; we thus performed additional analyses to show the robustness of the retrieved planetary parameters. With a low bulk density of $1.03\pm0.23~\mathrm{g\:cm^{-3}}$ and orbiting a bright host star ($J=8.3$, $V=9.6$), TOI-1710$\:$b is one of the best targets in this mass-radius range (near the Neptunian desert) for atmospheric characterization via transmission spectroscopy, a key measurement in constraining planet formation and evolutionary models of sub-Jovian planets., Comment: 18 pages, 16 figures, 5 tables, A&A in press

Aims: We investigate the photometric properties of the M7.5 equal-mass binary VHS J1256-1257AB, which, combined with the late-L dwarf VHS J1256-1257 b, forms one of the few young triple systems of ultra-cool dwarfs currently known. Methods: We analyzed two-minute TESS and two-second Spitzer archival data with total durations of about 25 days and 36 hours, respectively. Typical precision in the data is $\pm$1.5 % for TESS and $\pm$0.1 % (in 1 minute) for Spitzer. Results: The optical and infrared light curves periodically exhibit epochs of quasi-sinusoidal modulation followed by epochs of stochastic variability, which resembles the beat pattern created by two waves of similar frequencies that interfere with each other. Our two-wave model for the TESS data shows that the components of VHS J1256-1257AB rotate with periods of $2.0782\pm0.0004$ h and $2.1342\pm0.0003$ h, which is also supported by the Spitzer observations. As a result, the fluxes of the equally bright VHS J1256-1257A and B alternate between states of phase and anti-phase, explaining the observed photometric variability in their combined light. The projected spectroscopic velocity of VHS J1256-1257AB is remarkably similar to those obtained by combining the measured rotation periods and the expected radii, which indicates that the spin axes of VHS J1256-1257A and B are likely inclined at nearly 90 deg, as previously reported for VHS J1256-1257 b., Comment: Accepted for publication in A&A Letters

Aims. We present the first detailed analysis of the astrophysical parameters of the poorly studied Sco-Cen member HD 152384 and its circumstellar environment. Methods. We analyze newly obtained optical-near-IR XSHOOTER spectra, as well as archival TESS data, of HD 152384. In addition, we use literature photometric data to construct a detailed spectral energy distribution (SED) of the star. Results. The photospheric absorption lines in the spectrum of HD 152384 are characteristic of a A0 V star, for which we derive a stellar mass of 2.1 +/- 0.1 M_sun and a stellar age > 4.5 Myr. Superimposed on the photospheric absorption, the optical spectrum also displays double-peaked emission lines of Ca II, Fe I, Mg I and Si I, typical of circumstellar disks. Notably, all Hydrogen and Helium lines appear strictly in absorption. A toy model shows that the observed emission line profiles can be reproduced by emission from a compact (radius < 0.3 au) disk seen at an inclination of ~24 degrees. Further evidence for the presence of circumstellar material comes from the detection of a moderate infrared excess in the SED, similar to those found in extreme debris disk systems. Conclusions. We conclude that HD 152384 is surrounded by a tenuous circumstellar disk which, although rich in refractory elements, is highly depleted of volatile elements. To the best of our knowledge such a disk is unique within the group of young stars. However, it is reminiscent of the disks seen in some white dwarfs, which have been attributed to the disruption of rocky planets. We suggest that the disk around HD 152384 may have a similar origin and may be due to collisions in a newly formed planetary system., Comment: 5 pages, 5 figures, accepted for publication in A&A Letters

We present the discovery of rapid photometric variability in three ultra-cool dwarfs from long-duration monitoring with the Spitzer Space Telescope. The T7, L3.5, and L8 dwarfs have the shortest photometric periods known to date: ${1.080}^{+0.004}_{-0.005}$ h, ${1.14}^{+0.03}_{-0.01}$ h, and ${1.23}^{+0.01}_{-0.01}$ h, respectively. We confirm the rapid rotation through moderate-resolution infrared spectroscopy, which reveals projected rotational velocities between 79 and 104 km s$^{-1}$. We compare the near-infrared spectra to photospheric models to determine the objects' fundamental parameters and radial velocities. We find that the equatorial rotational velocities for all three objects are $\gtrsim$100 km s$^{-1}$. The three L and T dwarfs reported here are the most rapidly spinning and likely the most oblate field ultra-cool dwarfs known to date. Correspondingly, all three are excellent candidates for seeking auroral radio emission and net optical/infrared polarization. As of this writing, 78 L-, T-, and Y-dwarf rotation periods have now been measured. The clustering of the shortest rotation periods near 1 h suggests that brown dwarfs are unlikely to spin much faster., Comment: 35 pages, 13 figures, 6 tables, accepted for publication in the Astronomical Journal, typos corrected in updated version

Mid-infrared imaging traces the sub-micron and micron sized dust grains in protoplanetary disks and it offers constraints on the geometrical properties of the disks and potential companions, particularly if those companions have circumplanetary disks. We use the VISIR instrument and its upgrade NEAR on the VLT to take new mid-infrared images of five (pre-)transition disks and one circumstellar disk with proposed planets and obtain the deepest resolved mid-infrared observations to date in order to put new constraints on the sizes of the emitting regions of the disks and the presence of possible companions. We derotate and stack the data to find the disk properties. Where available we compare the data to ProDiMo (Protoplanetary Disk Model) radiation thermo-chemical models to achieve a deeper understanding of the underlying physical processes within the disks. We apply the circularised PSF subtraction method to find upper limits on the fluxes of possible companions and model companions with circumplanetary disks. We resolve three of the six disks and calculate position angles, inclinations and (upper limits to) sizes of emission regions in the disks, improving upper limits on two of the unresolved disks. In all cases the majority of the mid-IR emission comes from small inner disks or the hot inner rims of outer disks. We refine the existing ProDiMo HD 100546 model SED fit in the mid-IR by increasing the PAH abundance relative to the ISM, adopting coronene as the representative PAH, and increase the outer cavity radius to 22.3 AU. We produce flux estimates for putative planetary-mass companions and circumplanetary disks, ruling out the presence of planetary-mass companions with $L > 0.0028 L_{\odot}$ for $a > 180$ AU in the HD 100546 system. Upper limits of 0.5 mJy-30 mJy are obtained at 8 $\mu$m-12 $\mu$m for potential companions in the different disks., Comment: Accepted in A&A

We present 33 transit minimum times of 20 transiting planets discovered by the CoRoT mission, which have been obtained from ground-based observations since the mission's end in 2012, with the objective to maintain the ephemeris of these planets. Twelve of the observed planets are in the CoRoT fields near the galactic center and the remaining eight planets are in the fields near the anticenter. We detect indications for significant transit timing variations in the cases of CoRoT 3b, 11b, 13b, 27b. For two more planets (CoRoT 18b and 20b) we conclude that timing offsets in early follow-up observations led to ephemeris in discovery publications that are inconsistent with timings from follow-up observations in later epochs. In the case of CoRoT-20b, this might be due to the influence from a further non-transiting planet. We also note that a significant majority (23 of 33) of our reported minimum times have negative O-C values, albeit most of them are within the expected uncertainty of the ephemeris., Comment: Accepted by JAAVSO. 26 pages including two appendices

Rotational modulations of emission spectra in brown dwarf and exoplanet atmospheres show that clouds are often distributed non-uniformly in these ultracool atmospheres. The spatial heterogeneity in cloud distribution demonstrates the impact of atmospheric dynamics on cloud formation and evolution. In this study, we update the Hubble Space Telescope (HST) time-series data analysis of the previously reported rotational modulations of WISEP J004701+680352 -- an unusually red late-L brown dwarf with a spectrum similar to that of the directly imaged planet HR8799e. We construct a self-consistent spatially heterogeneous cloud model to explain the Hubble Space Telescope and the Spitzer time-series observations, as well as the time-averaged spectra of WISE0047. In the heterogeneous cloud model, a cloud thickness variation of around one pressure scale height explains the wavelength dependence in the HST near-IR spectral variability. By including disequilibrium CO/$CH_4$ chemistry, our models also reproduce the redder $J-K_{\rm s}$ color of WISE0047 compared to that of field brown dwarfs. We discuss the impact of vertical cloud structure on atmospheric profile and estimate the minimum eddy diffusivity coefficient for other objects with redder colors. Our data analysis and forward modeling results demonstrate that time-series spectrophotometry with a broad wavelength coverage is a powerful tool for constraining heterogeneous atmospheric structure., Comment: accepted for publication in The Astrophysical Journal

HD106906b is an ~11$M_{\mathrm{Jup}}$, ~15Myr old directly-imaged exoplanet orbiting at an extremely large distance from its host star. The wide separation (7.11 arcsec) between HD106906b and its host star greatly reduces the difficulty in direct-imaging observations, making it one of the most favorable directly-imaged exoplanets for detailed characterization. In this paper, we present HST/WFC3/IR time-resolved observations of HD106906b in the F127M, F139M, and F153M bands. We have achieved ~1% precision in the lightcurves in all three bands. The F127M lightcurve demonstrates marginally-detectable ($2.7\sigma$ significance) variability with a best-fitting period of 4 hr, while the lightcurves in the other two bands are consistent with flat lines. We construct primary-subtracted deep images and use these images to exclude additional companions to HD106906 that are more massive than 4$M_{\mathrm{Jup}}$ and locate at projected distances of more than ~500 au. We measure the astrometry of HD106906b in two HST/WFC3 epochs and achieve precisions better than 2.5 mas. The position angle and separation measurements do not deviate from those in the 2004 HST/ACS/HRC images for more than $1\sigma$ uncertainty. We provide the HST/WFC3 astrometric results for 25 background stars that can be used as reference sources in future precision astrometry studies. Our observations also provide the first 1.4-micron water band photometric measurement for HD106906b. HD106906b's spectral energy distribution and the best-fitting BT-Settl model have an inconsistency in the 1.4-micron water absorption band, which highlights the challenges in modeling atmospheres of young planetary-mass objects., Comment: Accepted for publication to AJ

Among the greatest challenges in understanding ultra-cool brown dwarf and exoplanet atmospheres is the evolution of cloud structure as a function of temperature and gravity. In this study, we present the rotational modulations of GU Psc b -- a rare mid-T spectral type planetary-mass companion at the end of the L/T spectral type transition. Based on the HST/WFC3 1.1-1.67$\rm\, \mu m$ time-series spectra, we observe a quasi-sinusoidal light curve with a peak-to-trough flux variation of 2.7 % and a minimum period of eight hours. The rotation-modulated spectral variations are weakly wavelength-dependent, or largely gray between 1.1-1.67$\rm\,\mu$m. The gray modulations indicate that heterogeneous clouds are present in the photosphere of this low-gravity mid-T dwarf. We place the color and brightness variations of GU Psc b in the context of rotational modulations reported for mid-L to late-T dwarfs. Based on these observations, we report a tentative trend: mid-to-late T dwarfs become slightly redder in $J-H$ color with increasing $J$-band brightness, while L dwarfs become slightly bluer with increasing brightness. If this trend is verified with more T-dwarf samples, it suggests that in addition to the mostly gray modulations, there is a second-order spectral-type dependence on the nature of rotational modulations., Comment: 15 pages, 7 figures, accepted for publication in AJ

We use the Wide Field Camera 3 on the {\sl Hubble Space Telescope} to spectrophotometrically monitor the young L7.5 companion HD~203030B. Our time series reveal photometric variability at 1.27\,$\mu$m and 1.39\,$\mu$m on time scales compatible with rotation. We find a rotation period of $7.5^{+0.6}_{-0.5}$ h: comparable to those observed in other brown dwarfs and planetary-mass companions younger than 300 Myr. We measure variability amplitudes of $1.1\pm0.3\%$ (1.27\,$\mu$m) and $1.7\pm0.4\%$ (1.39\,$\mu$m), and a phase lag of 56$^\circ\pm$28$^\circ$ between the two light curves. We attribute the difference in photometric amplitudes and phases to a patchy cloud layer that is sinking below the level where water vapor becomes opaque. HD 203030B and the few other known variable young late-L dwarfs are unlike warmer (earlier-type and/or older) L dwarfs, for which variability is much less wavelength-dependent across the 1.1--1.7$\mu$m region. We further suggest that a sinking of the top-most cloud deck below the level where water or carbon monoxide gas become opaque may also explain the often enhanced variability amplitudes of even earlier-type low-gravity L dwarfs. Because these condensate and gas opacity levels are already well-differentiated in T dwarfs, we do not expect the same variability amplitude enhancement in young vs.\ old T dwarfs., Comment: Accepted for publication in The Astrophysical Journal

Measurements of photometric variability at different wavelengths provide insights into the vertical cloud structure of brown dwarfs and planetary-mass objects. In seven Hubble Space Telescope consecutive orbits, spanning $\sim$10 h of observing time}, we obtained time-resolved spectroscopy of the planetary-mass T8-dwarf Ross 458C using the near-infrared Wide Field Camera 3. We found spectrophotometric variability with a peak-to-peak signal of 2.62$\pm$0.02 % (in the 1.10-1.60~$\mu$m white light curve). Using three different methods, we estimated a rotational period of 6.75$\pm$1.58~h for the white light curve, and similar periods for narrow $J$- and $H$- band light curves. Sine wave fits to the narrow $J$- and $H$-band light curves suggest a tentative phase shift between the light curves with wavelength when we allow different periods between both light curves. If confirmed, this phase shift may be similar to the phase shift detected earlier for the T6.5 spectral type 2MASS J22282889-310262. We find that, in contrast with 2M2228, the variability of Ross~458C shows evidence for a {color trend} within the narrow $J$-band, but gray variations in the narrow $H$-band. The spectral time-resolved variability of Ross 458C might be potentially due to heterogeneous sulfide clouds in the atmosphere of the object. Our discovery extends the study of spectral modulations of condensate clouds to the coolest T dwarfs, planetary-mass companions., Comment: Accepted in ApJL

We obtained linear polarization photometry ($J$-band) and low-resolution spectroscopy ($ZJ$-bands) of Trappist-1, which is a planetary system formed by an M8-type low-mass star and seven temperate, Earth-sized planets. The photopolarimetric monitoring campaign covered 6.5 h of continuous observations including one full transit of planet Trappist-1d and partial transits of Trappist-1b and e. The spectrophotometric data and the photometric light curve obtained over epochs with no planetary transits indicate that the low-mass star has very low level of linear polarization compatible with a null value. However, the "in transit" observations reveal an enhanced linear polarization signal with peak values of $p^* = 0.1\,\%$ with a confidence level of 3 $\sigma$, particularly for the full transit of Trappist-1d, thus confirming that the atmosphere of the M8-type star is very likely dusty. Additional observations probing different atmospheric states of Trappist-1 are needed to confirm our findings, as the polarimetric signals involved are low. If confirmed, polarization observations of transiting planetary systems with central ultra-cool dwarfs can become a powerful tool for the characterization of the atmospheres of the host dwarfs and the validation of transiting planet candidates that cannot be corroborated by any other method., Comment: Accepted for publication in MNRAS Letters

Bayesian atmospheric retrieval tools can place constraints on the properties of brown dwarfs and hot Jupiters atmospheres. To fully exploit these methods, high signal-to-noise spectral libraries with well-understood uncertainties are essential. We present a high signal-to-noise spectral library (1.10-1.69 microns) of the thermal emission of 76 brown dwarfs and hot Jupiters. All our spectra have been acquired with the Hubble Space Telescope's Wide Field Camera 3 instrument and its G141 grism. The near-infrared spectral types of these objects range from L4 to Y1. Eight of our targets have estimated masses below the deuterium-burning limit. We analyze the database to identify peculiar objects and/or multiple systems, concluding that this sample includes two very-low-surface-gravity objects and five intermediate-surface-gravity objects. In addition, spectral indices designed to search for composite atmosphere brown dwarfs, indicate that eight objects in our sample are strong candidates to have such atmospheres. None of these objects are overluminous, thus their composite atmospheres are unlikely a companion-induced artifact. Five of the eight confirmed candidates have been reported as photometrically variable, suggesting that composite atmospheric indices are useful in identifying brown dwarfs with strongly heterogeneous cloud covers. We compare hot Jupiters and brown dwarfs in a near-infrared color-magnitude diagram. We confirm that the coldest hot Jupiters in our sample have spectra similar to mid-L dwarfs, and the hottest hot Jupiters have spectra similar to those of M-dwarfs. Our sample provides a uniform dataset of a broad range of ultracool atmospheres, allowing large-scale, comparative studies, and providing a HST legacy spectral library.

Time-resolved observations of brown dwarfs' rotational modulations provide powerful insights into the properties of condensate clouds in ultra-cool atmospheres. Multi-wavelength light curves reveal cloud vertical structures, condensate particle sizes, and cloud morphology, which directly constrain condensate cloud and atmospheric circulation models. We report results from Hubble Space Telescope/Wide Field Camera 3 near-infrared G141 taken in six consecutive orbits observations of HN Peg B, an L/T transition brown dwarf companion to a G0V type star. The best-fit sine wave to the $1.1-1.7\mu$m broadband light curve has the amplitude of $1.206\pm0.025\%$ and period of $15.4\pm0.5$ hr. The modulation amplitude has no detectable wavelength dependence except in the 1.4 $\mu$m water absorption band, indicating that the characteristic condensate particle sizes are large ($>1\mu$m). We detect significantly ($4.4\sigma$) lower modulation amplitude in the 1.4$\mu$m water absorption band, and find that HN Peg B's spectral modulation resembles those of early T type brown dwarfs. We also describe a new empirical interpolation method to remove spectral contamination from the bright host star. This method may be applied in other high-contrast time-resolved observations with WFC3., Comment: Accepted for publication in AAS Journal

Upon its discovery in 2006, the young L7.5 companion to the solar analog HD 203030 was found to be unusual in being $\approx$200 K cooler than older late-L dwarfs. HD 203030B offered the first clear indication that the effective temperature at the L-to-T spectral type transition depends on surface gravity: now a well-known characteristic of low-gravity ultra-cool dwarfs. An initial age analysis of the G8V primary star indicated that the system was 130--400 Myr old, and so the companion between 12--31 $M_{\rm Jup}$. Using moderate resolution near-infrared spectra of HD 203030B, we now find features of very low gravity comparable to those of 10--150 Myr-old L7--L8 dwarfs. We also obtained more accurate near infrared and {\sl Spitzer}/IRAC photometry, and find a $(J-K)_{\rm MKO}$ color of $2.56\pm0.13$ mag---comparable to those observed in other young planetary-mass objects---and a luminosity of log($L_{\rm bol}/L_{\odot}$)$\,=\,-4.75\pm0.04$ dex. We further reassess the evidence for the young age of the host star, HD 203030, with a more comprehensive analysis of the photometry and updated stellar activity measurements and age calibrations. Summarizing the age diagnostics for both components of the binary, we adopt an age of 100 Myr for HD 203030B and an age range of 30--150 Myr. Using cloudy evolutionary models, the new companion age range and luminosity result in a mass of 11 $M_{\rm Jup}$ with a range of 8--15 $M_{\rm Jup}$, and an effective temperature of $1040\pm50$ K., Comment: 12 pages, 7 figures, accepted for publication in AJ

Observations of rotational modulations of brown dwarfs and giant exoplanets allow the characterization of condensate cloud properties. As of now rotational spectral modulations have only been seen in three L-type brown dwarfs. We report here the discovery of rotational spectral modulations in LP261-75B, an L6-type intermediate surface gravity companion to an M4.5 star. As a part of the Cloud Atlas Treasury program we acquired time-resolved Wide Field Camera 3 grism spectroscopy (1.1--1.69~$\mu$m) of LP261-75B. We find gray spectral variations with the relative amplitude displaying only a weak wavelength dependence and no evidence for lower-amplitude modulations in the 1.4~$\mu$m water band than in the adjacent continuum. The likely rotational modulation period is 4.78$\pm$0.95 h, although the rotational phase is not well sampled. The minimum relative amplitude in the white light curve measured over the whole wavelength range is 2.41$\pm$0.14\%. We report an unusual light curve with seemingly three peaks approximately evenly distributed in rotational phase. The spectral modulations suggests that the upper atmosphere cloud properties in {LP261-75B} are similar to two other mid-L dwarfs of typical infrared colors, but differ from that of the extremely red L-dwarf WISE0047.

We used the optical and near-infrared imagers located on the Liverpool, the IAC80, and the William Herschel telescopes to monitor 18 M7$-$L9.5 dwarfs with the objective of measuring their rotation periods. We achieved accuracies typically in the range $\pm$1.5$-$28 mmag by means of differential photometry, which allowed us to detect photometric variability at the 2$\sigma$ level in the 50\% of the sample. We also detected periodic modulation with periods in the interval 1.5$-$4.4 h in 9 out of 18 dwarfs that we attribute to rotation. Our variability detections were combined with data from the literature; we found that 65$\,\pm\,$18 $\%$ of M7$-$L3.5 dwarfs with $v\,$sin$\,i\ge30$ km s$^{-1}$ exhibit photometric variability with typical amplitudes $\le$20 mmag in the $I$-band. For those targets and field ultra-cool dwarfs with measurements of $v\,$sin$\,i$ and rotation period we derived the expected inclination angle of their rotation axis, and found that those with $v\,$sin$\,i\ge30$ km s$^{-1}$ are more likely to have inclinations $\gtrsim40$ deg. In addition, we used these rotation periods and others from the literature to study the likely relationship between rotation and linear polarization in dusty ultra-cool dwarfs. We found a correlation between short rotation periods and large values of linear polarization at optical and near-infrared wavelengths., Comment: 19 pages, 12 figures, accepted for publication in MNRAS

We present the final results from a targeted search for brown dwarfs with unusual near-infrared colors. From a positional cross-match of SDSS, 2MASS and WISE, we have identified 144 candidate peculiar L and T dwarfs. Spectroscopy confirms that 20 of the objects are peculiar or are candidate binaries. Nine of the 420 objects in our sample are young ($\lesssim$200 Myr; 2.1%) and another 8 (1.9%) are unusually red with no signatures of youth. With a spectroscopic $J-K_s$ color of 2.58 $\pm$ 0.11 mag, one of the new objects, the L6 dwarf 2MASS J03530419+0418193, is among the reddest field dwarfs currently known and is one of the reddest objects with no signatures of youth known to date. We have also discovered another potentially very low gravity object, the L1 dwarf 2MASS J00133470+1109403, and independently identified the young L7 dwarf 2MASS J00440332+0228112, first reported by Schneider and collaborators. Our results confirm that signatures of low gravity are no longer discernible in low to moderate resolution spectra of objects older than $\sim$200 Myr. The 1.9% of unusually red L dwarfs that do not show other signatures of youth could be slightly older, up to $\sim$400 Myr. In this case a red $J-K_s$ color may be more diagnostic of moderate youth than individual spectral features. However, its is also possible that these objects are relatively metal-rich, and so have an enhanced atmospheric dust content., Comment: 27 pages, 7 figures, 5 tables, accepted to AJ

Recent photometric studies have revealed that surface spots that produce flux variations are present on virtually all L and T dwarfs. Their likely magnetic or dusty nature has been a much-debated problem, the resolution to which has been hindered by paucity of diagnostic multi-wavelength observations. To test for a correlation between magnetic activity and photometric variability, we searched for H$\alpha$ emission among eight L3$-$T2 ultra-cool dwarfs with extensive previous photometric monitoring, some of which are known to be variable at 3.6 $\mu$m or 4.5 $\mu$m. We detected H$\alpha$ only in the non-variable T2 dwarf 2MASS J12545393$-$0122474. The remaining seven objects do not show H$\alpha$ emission, even though six of them are known to vary photometrically. Combining our results with those for 86 other L and T dwarfs from the literature show that the detection rate of H$\alpha$ emission is very high (94$\%$) for spectral types between L0 and L3.5 and much smaller (20$\%$) for spectral types $\ge$L4, while the detection rate of photometric variability is approximately constant (30$\%-$55$\%$) from L0 to T8 dwarfs. We conclude that chromospheric activity, as evidenced by H$\alpha$ emission, and large-amplitude photometric variability are not correlated. Consequently, dust clouds are the dominant driver of the observed variability of ultra-cool dwarfs at spectral types at least as early as L0., Comment: 12 pages, 4 figures, accepted for publication in ApJ

Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases withthe degree of oblateness, which is inversely proportional to the surface gravity. We aimed to test the existence of optical linear polarization in a sample of bright young brown dwarfs, with spectral types between M6 and L2, observable from the Calar Alto Observatory, and cataloged previously as low gravity objects using spectroscopy. Linear polarimetric images were collected in I and R-band using CAFOS at the 2.2 m telescope in Calar Alto Observatory (Spain). The flux ratio method was employed to determine the linear polarization degrees. With a confidence of 3$\sigma$, our data indicate that all targets have a linear polarimetry degree in average below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were observed. We detected significant (i.e. P/$\sigma$ $\le$ 3) linear polarization for the young M6 dwarf 2MASS J04221413+1530525 in the R-band, with a degree of $\mathrm{p^{*}}$ = 0.81 $\pm$ 0.17 %., Comment: Accepted for publication in MNRAS

Our simultaneous three-colour ($BVR$) polarimetric observations of the low-mass black hole X-ray binary V404 Cyg show a small but statistically significant change of polarization degree ($\Delta p \sim 1$ per cent) between the outburst in June 2015 and the quiescence. The polarization of V404 Cyg in the quiescent state agrees within the errors with that of the visually close (1\farcs4) companion ($p_{R} = 7.3\pm 0.1$ per cent), indicating that it is predominantly of interstellar origin. The polarization pattern of the surrounding field stars supports this conclusion. From the observed variable polarization during the outburst we show that polarization degree of the intrinsic component peaks in the $V$-band, $p_{V} = 1.1\pm 0.1$ per cent, at the polarization position angle of $\theta_{V}= -7\deg\pm 2\deg$, which is consistent in all three passbands. We detect significant variations in the position angle of the intrinsic polarization in $R$ band from $-30\deg$ to $\sim 0\deg$ during the outburst peak. The observed wavelength dependence of the intrinsic polarization does not support non-thermal synchrotron emission from a jet as a plausible mechanism, but is in better agreement with the combined effect of electron (Thomson) scattering and absorption in a flattened plasma envelope or outflow surrounding the illuminating source. Alternatively, the polarization signal can be produced by scattering of the disc radiation in a mildly relativistic polar outflow. The position angle of the intrinsic polarization, nearly parallel to the jet direction (i.e. perpendicular to the accretion disc plane), is in agreement with these interpretations., Comment: 12 pages, 9 figures, 4 tables; Accepted to MNRAS

We aim to study the optical and near-infrared linear polarimetric properties of a sample of young M7-L7 dwarfs ($\approx$1-500 Myr) with spectroscopic signatures of low- and intermediate-gravity atmospheres. We collected optical ($RIZ$) and near-infrared ($YJHK_{\rm s}$) linear polarimetry images on various time scales from $\sim$0.2 h to months. Linear polarization degrees in the interval 0-1.5\% ($I$- and $J$-bands) were measured with accuracies ranging from $\pm$0.1 $\%$ to $\pm$0.9 $\%$ depending on the observing filter and the target brightness. We found that the young field dwarfs in our sample show similar polarimetric degrees at both $I$- and $J$-bands, and that there is no obvious trend with the spectral type. The two Taurus sources in our sample show intense levels of $J$-band linear polarization probably due to surrounding disks. By compiling data from the literature for high-gravity M7-L7 dwarfs with likely ages $\ge$500 Myr, we did not observe any apparent difference in the linear polarimetry intensity between the young and old samples that could be ascribed to differing atmospheric gravities. Polarimetric variability with peak to peak amplitudes up to 1.5 $\%$ is detected on scales of about a rotation in two out of four targets that were monitored over several hours. Long-term polarimetric variability is also detected in nearly all dwarfs of the sample with data spanning months to years., Comment: 16 pages, 9 figures, accepted in MNRAS

We present the discovery of a variable optical counterpart to the unidentified gamma-ray source 3FGL J0212.1+5320, and argue this is a new compact binary millisecond pulsar (MSP) candidate. We show 3FGL J0212.1+5320 hosts a semi-detached binary with a 0.86955$\pm$0.00015 d orbital period and a F6-type companion star at an estimated distance of D=1.1$\pm$0.2 kpc, with a radial velocity curve semi-amplitude K$_2$=214.1$\pm$5.0 km s$^{-1}$ and a projected rotational velocity of Vsin(i)=73.2$\pm$1.6 km s$^{-1}$. We find a hard X-ray source at the same location with a 0.5$-$10 keV luminosity L$_\mathrm{X}$=2.6$\times$10$^{32}$ (D/1.1 kpc)$^2$ erg s$^{-1}$, which strengthens the MSP identification. Our results imply a mass ratio q=M$_2$/M$_1$=0.26$^{+0.02}_{-0.03}$ if the companion star fills its Roche lobe, and q$\gtrsim$0.26 in any case. This classifies 3FGL J0212.1+5320 as a "redback" binary MSP; if its MSP nature is confirmed, this will be the brightest compact binary MSP in the optical band (r'$\simeq$14.3 mag) and will have the longest orbital period among Galactic field systems (nearly 21 hr). Based on the light curve peak-to-peak amplitude ($\Delta$r=0.19 mag), we further suggest that the orbital inclination is high and the putative pulsar mass is close to canonical (M$_1$$\simeq$1.3$-$1.6 M$_\odot$). Finally, we discuss the lack of heating signatures and asymmetric optical light curves in the context of other redback MSPs., Comment: Accepted for publication in MNRAS; 9 pages, 8 figures, minor changes after referee suggestions

The Earth's albedo is a fundamental climate parameter for understanding the radiation budget of the atmosphere. It has been traditionally measured from space platforms, but also from the ground for sixteen years from Big Bear Solar Observatory by observing the Moon. The photometric ratio of the dark (earthshine) to the bright (moonshine) sides of the Moon is used to determine nightly anomalies in the terrestrial albedo, with the aim is of quantifying sustained monthly, annual and/or decadal changes. We find two modest decadal scale cycles in the albedo, but with no significant net change over the sixteen years of accumulated data. Within the evolution of the two cycles, we find periods of sustained annual increases, followed by comparable sustained decreases in albedo. The evolution of the earthshine albedo is in remarkable agreement with that from the CERES instruments, although each method measures different slices of the Earth's Bond albedo., Comment: Accepted for publication in Geophysical Research Letters

Aims: We aimed to monitor the optical linear polarimetric signal of the magnetized, rapidly rotating M8.5 dwarf TVLM 513$-$46546. Methods: $R$- and $I$-band linear polarimetry images were collected with the ALFOSC instrument of the 2.56-m Nordic Optical Telescope on two consecutive nights covering about 0.5 and 4 rotation cycles in the $R$ and $I$ filters, respectively. We also obtained simultaneous intensity curves by means of differential photometry. The typical precision of the data is $\pm$0.46\% ($R$), $\pm$0.35\% ($I$) in the linear polarization degree and $\pm$9 mmag ($R$), $\pm$1.6 mmag ($I$) in the differential intensity curves. Results: Strong and variable linear polarization is detected in the $R$ and $I$ filters, with values of maximum polarization ($p^{*}$ = 1.30$\pm$0.35 \%) similar for both bands. The intensity and the polarimetric curves present a sinusoid-like pattern with a periodicity of $\sim$1.98 h, which we ascribe to structures in TVLM 513$-$46's surface synchronized with rotation. We found that the peaks of the intensity and polarimetric curves occur with a phase difference of 0.18$\pm$0.01, and that the maximum of the linear polarization happens nearly half a period (0.59$\pm$0.03) after the radio pulse. We discussed different scenarios to account for the observed properties of the light curves., Comment: Accepted for publication in Astronomy and Astrophysics

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from $\sim$0\% to 1.3\%, are suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with $T_{\rm eff} \simeq 3800$ K. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant "bump" just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet's Hill sphere and effectively undergo `Roche lobe overflow,' even though the planet's surface is likely underfilling its Roche lobe by a factor of 2., Comment: 22 pages, 16 figures. Final version accepted to ApJ

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? What causes the exceptional diversity observed as compared to the Solar System? EChO (Exoplanet Characterisation Observatory) has been designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large and diverse planet sample within its four-year mission lifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300K-3000K) of F to M-type host stars. Over the next ten years, several new ground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO's launch and enable the atmospheric characterisation of hundreds of planets. Placing the satellite at L2 provides a cold and stable thermal environment, as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. A 1m class telescope is sufficiently large to achieve the necessary spectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16 micron) and SNR to be achieved by EChO, thanks to its high stability and dedicated design, would enable a very accurate measurement of the atmospheric composition and structure of hundreds of exoplanets., Comment: 50 pages, 30 figures. Experimental Astronomy

(Abridged) We report on the near-infrared low-resolution spectroscopy and red optical (Z-band) photometry of seven proper-motion, very low-mass substellar member candidates of the Pleiades cluster with magnitudes in the interval J=17.5-20.8 and K=16.1-18.5 mag. Spectra were acquired for six objects with the LIRIS and NIRSPEC instruments mounted on the 4.2-m WHT and the 10-m Keck II telescopes. Z-band images of two of the faintest candidates were collected with ACAM/WHT. The new data confirm the low temperatures of all seven Pleiades candidates. From the imaging observations, we find extremely red Z-J and Z-K colors that suggest that the faintest target, Calar Pleiades 25, has a Galactic rather than extragalactic nature. We tentatively classify the spectroscopic targets from early-L to ~T0 and suggest that the L/T transition, which accounts for the onset of methane absorption at 2.1 micron, may take place at J,K ~ 20.3, 17.8 mag in the Pleiades (absolute values of M_J ~ 14.7 and M_K ~ 12.2 mag). We find evidence of likely low-gravity atmospheres based on the presence of triangular-shape H-band fluxes and the high flux ratio K/H (compatible with red H-K colors) of Calar Pleiades 20, 21, and 22, which is a feature also seen in field low-gravity dwarfs. Weak KI absorption lines at around 1.25 micron are probably seen in two targets. These observations add support to the cluster membership of all seven objects in the Pleiades. The trend delineated by the spectroscopic sequence of Pleiades late-M and L dwarfs resembles that of the field. With masses estimated at 0.012-0.015 Msol (solar metallicity and 120 Myr), Calar Pleiades 20 (L6 +/- 1), 21 (L7 +/- 1), and 22 (L/T) may become the coolest and least massive Pleiades members that are corroborated with photometry, astrometry, and spectroscopy. Calar Pleiades 25 (<0.012 Msol) is a firm free-floating planetary-mass candidate in the Pleiades., Comment: Accepted for publication in A&A Letters

(Abridged) We aim to determine the trigonometric parallaxes and proper motions of a sample of ten field L0-L5 dwarfs with spectroscopic evidence for low-gravity atmospheres. We obtained J and Ks imaging data using 2-4-m class telescopes with a typical cadence of one image per month between 2010 January and 2012 December. We also obtained low resolution optical spectra (R~300, 500-1100 nm) using the 10-m GTCs to assess the presence of lithium absorption in four targets and confirm their young age. Trigonometric parallaxes and proper motions were derived to typical accuracies of 1 mas and +/-10 mas/yr. All ten L dwarfs have large motions, and are located at distances between 9 and 47 pc. They lie above and on the sequence of field dwarfs in the absolute J and K_s magnitude versus spectral type and luminosity versus Teff diagrams, implying ages similar to or smaller than those typical of the field. The detection of atomic lithium in the atmosphere of 2MASS J00452143+1634446 is reported for the first time. Three dwarfs have locations in the HR diagram indicative of old ages and high masses consistent with the observed lithium depletion previously published. We did not find evidence for the presence of astrometric companions with minimum detectable masses typically >=25 Mjup and face-on, circular orbits with periods between 60-90 d and 3 yr around eight targets. The astrometric and spectroscopic data indicate that about 60-70% of the field L-type dwarfs in our sample with evidence for low-gravity atmospheres are indeed young-to-intermediate-age brown dwarfs of the solar neighborhood with expected ages and masses in the intervals 10-500 Myr and 11-45 Mjup. The peaked-shape of the H-band spectra of L dwarfs, a signpost of youth, appears to be present up to ages of 120-500 Myr and intermediate-to-high gravities., Comment: Accepted for publication in A&A

Aims: We aim to extend our current observational understanding of the integrated planet Earth spectropolarimetry from the optical to the near-infrared wavelengths. Major biomarkers like O$_{\rm 2}$ and water vapor are strong flux absorbents in the Earth atmosphere and some linear polarization of the reflected stellar light is expected to occur at these wavelengths. Methods: Simultaneous optical ($0.4-0.9$ $\mu$m) and near-infrared ($0.9-2.3$ $\mu$m) linear spectropolarimetric data of the earthshine were acquired by observing the nightside of the waxing Moon. The data have sufficient spectral resolution (2.51 nm in the optical, and 1.83 and 2.91 nm in the near-infrared) to resolve major molecular species present in the Earth atmosphere. Results: We find the highest values of linear polarization ($\ge 10\%$) at the bluest wavelengths, which agrees with the literature. Linear polarization intensity steadily decreases towards red wavelengths reaching a nearly flat value beyond $\sim$0.8 $\mu$m. In the near-infrared, we measured a polarization degree of $\sim4.5 \%$ for the continuum. We report the detection of molecular features due to O$_{2}$ at $0.760, 1.25 \mu$m and H$_{2}$O at 0.653$-$0.725 $\mu$m, 0.780$-$0.825 $\mu$m, 0.93 and 1.12 $\mu$m in the spectropolarimetric data; most of them show high linear polarimetry degrees above the continuum. In particular, the broad H$_{2}$O 1.12 $\mu$m band displays a polarimetric intensity as high as that of the blue optical. These features may become a powerful tool to characterize Earth-like planets in polarized light., Comment: 4 pages, 3 figures. Accepted for publication as Letter in Astronomy and Astrophysics on 23/01/2014

Aims. We aim at studying the near infrared linear polarization signal of rapidly rotating ultracool dwarfs with spectral types ranging from M7 through T2 and projected rotational velocities vsini >= 30 km s^{-1}. All these dwarfs are believed to have dusty atmospheres and oblate shapes, an appropriate scenario to produce measurable linear polarization of the continuum light.\\ Methods. Linear polarimetric images were collected in the J-band for a sample of 18 fast-rotating ultracool dwarfs, five of which were also observed in the Z-band using the LIRIS spectrograph on the Cassegrain focus of the 4.2-m William Herschel Telescope. The measured median uncertainty in the linear polarization degree is +/-0.13% for our sample, which allowed us to detect polarization signatures above ~0.39% with a confidence of >=3\sigma.\\ Results. About 40+/-15% of the sample is linearly polarized in the Z- and J-bands. All positive detections have linear polarization degrees ranging from 0.4% to 0.8% in both filters independently of spectral type and spectroscopic rotational velocity. However, simple statistics point at the fastest rotators (vsini >=60 km s^{-1}) having a larger fraction of positive detections and a larger averaged linear polarization degree than the moderately rotating dwarfs (vsini=30--60 km s^{-1}). Our data suggest little linear polarimetric variability on short time scales (i.e., observations separated by a few ten rotation periods), and significant variability on long time scales (i.e., hundred to thousand rotation cycles), supporting the presence of "long-term weather" in ultracool dwarf atmospheres., Comment: 12 pages, 7 figures, recommended for publication in Astronomy and Astrophysics

Aims: With available Virtual Observatory tools, we looked for new M dwarfs in the solar neighbourhood and M giants with high tangential velocities. Methods: From an all-sky cross-match between the optical Tycho-2 and the near-infrared 2MASS catalogues, we selected objects with proper motions >50mas/yr and very red V-Ks colours. For the most interesting targets, we collected multi-wavelength photometry, constructed spectral energy distributions, estimated effective temperatures and surface gravities from fits to atmospheric models, performed time-series analysis of ASAS V-band light curves, and assigned spectral types from low-resolution spectroscopy obtained with CAFOS at the 2.2m Calar Alto telescope. Results: We got a sample of 59 bright red high proper-motion objects, including fifty red giants, four red dwarfs, and five objects reported in this work for the first time. The five new stars have magnitudes V~10.8-11.3mag, reduced proper motions midway between known dwarfs and giants, near-infrared colours typical of giants, and effective temperatures Teff~2900-3400K. From our time-series analysis, we discovered a long secondary period in Ruber 4 and an extremely long primary period in Ruber 6. With the CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of which seems to be one of the brightest metal-poor M giants ever identified., Comment: Accepted in Astronomy & Astrophysics