Detection of Hα emission from PZ Telescopii B using SPHERE/ZIMPOL

Hα is a powerful tracer of accretion and chromospheric activity, which has been detected in the case of young brown dwarfs and even recently in planetary mass companions (e.g. PDS70 b and c). Hα detections and characterisation of brown dwarf and planet companions can further our knowledge of their formation and evolution, and expanding such a sample is therefore our primary goal. We used the Zurich Imaging POLarimeter (ZIMPOL) of the SPHERE instrument at the Very Large Telescope (VLT) to observe the known 38−72 MJ companion orbiting PZ Tel, obtaining simultaneous angular differential imaging observations in both continuum and narrow Hα band. We detect Hα emission from the companion, making this only the second Hα detection of a companion using the SPHERE instrument. We used our newly added astrometric measurements to update the orbital analysis of PZ Tel B, and we used our photometric measurements to evaluate the Hα line flux. Given the estimated bolometric luminosity, we obtained an Hα activity (log(LHα/Lbol)) between −4.16 and −4.31. The Hα activity of PZ Tel B is consistent with known average activity levels for M dwarf of the same spectral type. Given the absence of a known gaseous disk and the relatively old age of the system (24 Myr), we conclude that the Hα emission around PZ Tel B is likely due to chromospheric activity.

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Hα Emission From Active Equal-Mass, Wide M Dwarf Binaries1

Publications of the Astronomical Society of the Pacific ◽

10.1086/679329 ◽

2014 ◽

Vol 126 (946) ◽

pp. 1081-1091 ◽

Cited By ~ 3

Author(s):

Heather C. Gunning ◽

Sarah J. Schmidt ◽

James R. A. Davenport ◽

Saurav Dhital ◽

Suzanne L. Hawley ◽

...

Keyword(s):

Equal Mass ◽

Hα Emission ◽

M Dwarf

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A Radial velocity survey of spatially resolved young, low-mass binaries

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732156 ◽

2018 ◽

Vol 618 ◽

pp. A5 ◽

Cited By ~ 2

Author(s):

Stephen Durkan ◽

Markus Janson ◽

Simona Ciceri ◽

Wolfgang Brandner ◽

Joshua Schlieder ◽

...

Keyword(s):

Radial Velocity ◽

Solar Neighborhood ◽

Activity Level ◽

Activity Levels ◽

Old Field ◽

Triple Systems ◽

Chromospheric Activity ◽

Low Mass ◽

Orbital Periods ◽

Moving Groups

The identification and characterisation of low-mass binaries is of importance for a range of astrophysical investigations. Low-mass binaries in young (∼10–100 Myr) moving groups (YMGs) in the solar neighborhood are of particular significance as they provide unique opportunities to calibrate stellar models and evaluate the ages and coevality of the groups themselves. Low-mass M-dwarfs have pre-main sequence life times on the order of ∼100 Myr and therefore are continually evolving along a mass-luminosity track throughout the YMG phase, providing ideal laboratories for precise isochronal dating, if a model-independent dynamical mass can be measured. AstraLux lucky imaging multiplicity surveys have recently identified hundreds of new YMG low-mass binaries, where a subsample of M-dwarf multiples have estimated orbital periods less than 50 yr. We have conducted a radial velocity survey of a sample of 29 such targets to complement the astrometric data. This will allow enhanced orbital determinations and precise dynamical masses to be derived in a shorter timeframe than possible with astrometric monitoring alone, and allow for a more reliable isochronal analysis. Here we present radial velocity measurements derived for our sample over several epochs. We report the detection of the three-component spectroscopic multiple 2MASS J05301858-5358483, for which the C component is a new discovery, and forms a tight pair with the B component. Originally identified as a YMG member, we find that this system is a likely old field interloper, whose high chromospheric activity level is caused by tidal spin-up of the tight BC pair. Two other triple systems with a tight pair exist in the sample, 2MASS J04244260-0647313 (previously known) and 2MASS J20163382-0711456, but for the rest of the targets we find that additional tidally synchronized companions are highly unlikely, providing further evidence that their high chromospheric activity levels are generally signatures of youth.

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Planet-disk interactions in HD 169142? Tracing ellipticity, structures, and offsets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318008281 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 241-243

Author(s):

Gesa H.-M. Bertrang ◽

Henning Avenhaus

Keyword(s):

Surface Brightness ◽

Broad Band ◽

Small Scale ◽

High Contrast ◽

Large Telescope ◽

Very Large Telescope ◽

Be Star ◽

Scale Structures ◽

Differential Imaging ◽

Small Scale Structures

AbstractIn Bertrang et al. (2018), we present new data of the protoplanetary disk surrounding the Herbig Ae/Be star HD 169142 obtained in the very broad-band (VBB) with the Zurich imaging polarimeter (ZIMPOL), a subsystem of the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE) at the Very Large Telescope (VLT). Our Polarimetric Differential Imaging (PDI) observations probe the disk as close as 0.″3 (3.5au) to the star and are able to trace the disk out to ~1.″08 (~126 au). We find an inner hole, a bright ring bearing substructures around ~0.″18 (21au), and an elliptically shaped gap stretching from 0.″25 to 0.″47 (29–55 au). Outside of 0.″47, the surface brightness drops off, discontinued only by a narrow annular brightness minimum at ~0.″63–0.″74 (74–87 au). These observations confirm features found in less-well resolved data as well as reveal yet undetected indications for planet-disk interactions, such as small-scale structures, star-disk offsets, and potentially moving shadows.

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GJ 357 b

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038280 ◽

2020 ◽

Vol 641 ◽

pp. A113

Author(s):

D. Modirrousta-Galian ◽

B. Stelzer ◽

E. Magaudda ◽

J. Maldonado ◽

M. Güdel ◽

...

Keyword(s):

Large Scale ◽

Systematic Errors ◽

Small Mass ◽

Activity Levels ◽

M Dwarfs ◽

X Ray ◽

History Of ◽

Age Relations ◽

M Dwarf ◽

Atmospheric Mass

Aims. In this paper we present a deep X-ray observation of the nearby M dwarf GJ 357 and use it to put constraints on the atmospheric evolution of its planet, GJ 357 b. We also analyse the systematic errors in the stellar parameters of GJ 357 in order to see how they affect the perceived planetary properties. Methods. By comparing the observed X-ray luminosity of its host star, we estimate the age of GJ 357 b as derived from a recent XMM-Newton observation (log Lx [erg s−1] = 25.73), with Lx− age relations for M dwarfs. We find that GJ 357 presents one of the lowest X-ray activity levels ever measured for an M dwarf, and we put a lower limit on its age of 5 Gyr. Using this age limit, we performed a backwards reconstruction of the original primordial atmospheric reservoir. Furthermore, by considering the systematic errors in the stellar parameters, we find a range of possible planetary masses, radii, and densities. Results. From the backwards reconstruction of the irradiation history of GJ 357 b’s we find that the upper limit of its initial primordial atmospheric mass is ~38 M⊕. An initial atmospheric reservoir significantly larger than this may have survived through the X-ray and ultraviolet irradiation history, which would not be consistent with current observations that suggest a telluric composition. However, given the relatively small mass of GJ 357 b, even accreting a primordial envelope ≳10 M⊕ would have been improbable as an unusually low protoplanetary disc opacity, large-scale migration, and a weak interior luminosity would have been required. For this reason, we discard the possibility that GJ 357 b was born as a Neptunian- or Jovian-sized body. In spite of the unlikelihood of a currently existing primordial envelope, volcanism and outgassing may have contributed to a secondary atmosphere. Under this assumption, we present three different synthetic IR spectra for GJ 357 b that one might expect, consisting of 100% CO2, 100% SO2, and 75% N2, 24% CO2 and 1% H2O, respectively. Future observations with space-based IR spectroscopy missions will be able to test these models. Finally, we show that the uncertainties in the stellar and planetary quantities do not have a significant effect on the estimated mass or radius of GJ 357 b.

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Mid-infrared evolution of η Carinae from 1968 to 2018

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936277 ◽

2019 ◽

Vol 630 ◽

pp. L6 ◽

Cited By ~ 2

Author(s):

A. Mehner ◽

W.-J. de Wit ◽

D. Asmus ◽

P. W. Morris ◽

C. Agliozzo ◽

...

Keyword(s):

Spectral Energy Distribution ◽

Circumstellar Dust ◽

Spectral Energy ◽

Short Term ◽

Dust Extinction ◽

Bolometric Luminosity ◽

Very Large Telescope ◽

Optical Wavelengths ◽

The Mean

η Car is one of the most luminous and massive stars in our Galaxy and is the brightest mid-IR source in the sky outside our solar system. Since the late 1990s, the central source has dramatically brightened at UV and optical wavelengths. This might be explained by a decrease in circumstellar dust extinction. We aim to establish the mid-IR flux evolution and further our understanding of the star’s UV and optical brightening. Mid-IR images from 8−20 μm were obtained in 2018 with VISIR at the Very Large Telescope. Archival data from 2003 and 2005 were retrieved from the ESO Science Archive Facility, and historical records were collected from publications. We present mid-IR images of η Car with the highest angular resolution to date at the corresponding wavelengths (≥0.22″). We reconstruct the mid-IR evolution of the spectral energy distribution of the spatially integrated Homunculus nebula from 1968 to 2018 and find no long-term changes. The bolometric luminosity of η Car has been stable over the past five decades. We do not observe a long-term decrease in the mid-IR flux densities that could be associated with the brightening at UV and optical wavelengths, but circumstellar dust must be declining in our line of sight alone. Short-term flux variations within about 25% of the mean levels could be present.

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Activity, Colour Anomalies and Temperature Determination in Solar-type Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100079860 ◽

1991 ◽

Vol 130 ◽

pp. 333-335

Author(s):

J. Fabregat ◽

V. Reglero ◽

J. Suso ◽

J.E. Armentia

Keyword(s):

Broad Band ◽

Activity Levels ◽

Temperature Determination ◽

Temperature Scales ◽

Chromospheric Activity ◽

Long Baseline ◽

Solar Type ◽

The Mean ◽

Reliable Temperature

The presence of photometric anomalies in broad band colours produced by chromospheric activity was first suggested by Campbell (1984). He defined the colour anomaly δ(B–V)V–K as the deviation from the mean relation (B–V)–(V–K) for Hyades dwarfs, and found this anomaly correlated well with several activity indicators.Since the work of Campbell, several authors have discussed the relation between activity and colour anomalies, obtaining diverging results. This discussion is relevant because long baseline photometric colours are the most reliable temperature indicators, and the presence of such anomalies implies that no consistent temperature scales can be obtained for stars with different activity levels. These topics have been recently reviewed by Soderblom (1989).

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12 years of stellar activity observations in Argentina

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312005029 ◽

2011 ◽

Vol 7 (S286) ◽

pp. 317-323 ◽

Cited By ~ 1

Author(s):

P. J. D. Mauas ◽

A. Buccino ◽

R. Díaz ◽

M. Vieytes ◽

R. Petrucci ◽

...

Keyword(s):

Spectral Range ◽

Conversion Factor ◽

Activity Levels ◽

Late Type ◽

Cyclic Activity ◽

Chromospheric Activity ◽

Activity Measurements ◽

Radiative Losses ◽

Hydrogen Lines ◽

Observational Program

AbstractWe present an observational program we started in 1999, to systematically obtain mid-resolution spectra of late-type stars, to study in particular chromospheric activity. In particular, we found cyclic activity in four dM stars, including Prox-Cen. We directly derived the conversion factor that translates the known S index to flux in the Ca II cores, and extend its calibration to a wider spectral range. We investigated the relation between the activity measurements in the calcium and hydrogen lines, and found that the usual correlation observed is the product of the dependence of each flux on stellar color, and it is not always preserved when simultaneous observations of a particular star are considered. We also used our observations to model the chromospheres of stars of different spectral types and activity levels, and found that the integrated chromospheric radiative losses, normalized to the surface luminosity, show a unique trend for G and K dwarfs when plotted against the S index.

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HOW TO CONSTRAIN YOUR M DWARF: MEASURING EFFECTIVE TEMPERATURE, BOLOMETRIC LUMINOSITY, MASS, AND RADIUS

The Astrophysical Journal ◽

10.1088/0004-637x/804/1/64 ◽

2015 ◽

Vol 804 (1) ◽

pp. 64 ◽

Cited By ~ 279

Author(s):

Andrew W. Mann ◽

Gregory A. Feiden ◽

Eric Gaidos ◽

Tabetha Boyajian ◽

Kaspar von Braun

Keyword(s):

Effective Temperature ◽

Bolometric Luminosity ◽

M Dwarf

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Searching for Hα emitting sources around MWC 758

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832874 ◽

2018 ◽

Vol 613 ◽

pp. L5 ◽

Cited By ~ 11

Author(s):

N. Huélamo ◽

G. Chauvin ◽

H. M. Schmid ◽

S. P. Quanz ◽

E. Whelan ◽

...

Keyword(s):

Adaptive Optics ◽

Mass Range ◽

Position Angle ◽

Central Star ◽

Young Star ◽

Upper Limit ◽

T Tauri ◽

Very Large Telescope ◽

Accretion Rates ◽

Differential Imaging

Context. MWC 758 is a young star surrounded by a transitional disk. The disk shows an inner cavity and spiral arms that could be caused by the presence of protoplanets. Recently, a protoplanet candidate has been detected around MWC 758 through high-resolution L′-band observations. The candidate is located inside the disk cavity at a separation of ~111 mas from the central star, and at an average position angle of ~165.5°. Aims. We aim at detecting accreting protoplanet candidates within the disk of MWC 758 through angular spectral differential imaging (ASDI) observations in the optical regime. In particular, we explore the emission at the position of the detected planet candidate. Methods. We have performed simultaneous adaptive optics observations in the Hα line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT). Results. The data analysis does not reveal any Hα signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5σ upper limit of ~7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a Hα line luminosity of LHα ≲ 5×10−5 L⊙ at 111 mas. Assuming that LHα scales with Lacc as in classical T Tauri stars (CTTSs) as a first approximation, we can estimate an accretion luminosity of Lacc < 3.7 × 10−4 L⊙ for the protoplanet candidate. For the predicted mass range of MWC 758b, 0.5–5 MJup, this implies accretion rates smaller than Ṁ < 3.4 × (10−8−10−9)M⊙ yr−1, for an average planet radius of 1.1 RJup. Therefore, our estimates are consistent with the predictions of accreting circumplanetary accretion models for Rin = 1RJup. The ZIMPOL line luminosity is consistent with the Hα upper limit predicted by these models for truncation radii ≲3.2 RJup. Conclusions. The non-detection of any Hα emitting source in the ZIMPOL images does not allow us to unveil the nature of the L′ detected source. Either it is a protoplanet candidate or a disk asymmetry.

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Compensatory variability in network parameters enhances memory performance in the Drosophila mushroom body

10.1101/2021.02.03.429444 ◽

2021 ◽

Author(s):

Nada Y. Abdelrahman ◽

Eleni Vasilaki ◽

Andrew C. Lin

Keyword(s):

Mushroom Body ◽

Neural Circuit ◽

Memory Performance ◽

Activity Levels ◽

Compensatory Mechanisms ◽

Network Parameters ◽

Kenyon Cells ◽

Average Activity ◽

Circuit Function ◽

Activity Dependent

AbstractNeural circuits use homeostatic compensation to achieve consistent behaviour despite variability in underlying intrinsic and network parameters. However, it remains unclear how compensation regulates variability across a population of the same type of neurons within an individual, and what computational benefits might result from such compensation. We address these questions in the Drosophila mushroom body, the fly’s olfactory memory center. In a computational model, we show that memory performance is degraded when the mushroom body’s principal neurons, Kenyon cells (KCs), vary realistically in key parameters governing their excitability, because the resulting inter-KC variability in average activity levels makes odor representations less separable. However, memory performance is rescued while maintaining realistic variability if parameters compensate for each other to equalize KC average activity. Such compensation can be achieved through both activity-dependent and activity-independent mechanisms. Finally, we show that correlations predicted by our model’s compensatory mechanisms appear in the Drosophila hemibrain connectome. These findings reveal compensatory variability in the mushroom body and describe its computational benefits for associative memory.Significance statementHow does variability between neurons affect neural circuit function? How might neurons behave similarly despite having different underlying features? We addressed these questions in neurons called Kenyon cells, which store olfactory memories in flies. Kenyon cells differ among themselves in key features that affect how active they are, and in a model of the fly’s memory circuit, adding this inter-neuronal variability made the model fly worse at learning the values of multiple odors. However, memory performance was rescued if compensation between the variable underlying features allowed Kenyon cells to be equally active on average, and we found the hypothesized compensatory variability in real Kenyon cells’ anatomy. This work reveals the existence and computational benefits of compensatory variability in neural networks.

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