Sky and Telescope - January 2018 - 11

Alcyone

1.0005

Pulsations in the Pleiades

1.0000
0.9995

Atlas

1.005
1.000
0.995

Electra

1.0005
1.0000

Relative brightness

STELLAR

0.9995

Maia

1.003
1.000
0.997

Merope

1.005
1.000
0.995

Taygeta

1.001
1.000
0.999

Pleione

1.005
1.000
0.9995

Days observed

THE EXOPLANET-HUNTING Kepler
spacecraft long monitored hundreds
of thousands of distant stars with
an exquisite sensitivity that - ironically - put the brightest stars out of
its reach. But not anymore: Publishing
in the November issue of The Monthly
Notices of the Royal Astronomical
Society, Timothy White (Aarhus
University, Denmark) and colleagues
tried out an innovative new technique
known as halo photometry on Kepler
observations of the brilliant "Seven
Sisters" of the Pleiades.
CCD cameras capture photons in
"wells," each of which corresponds
to a single pixel in the resulting
image. But a bright source can cause
a well to overﬂow, saturating the
central pixel(s) and creating a "bleed
trail." White and colleagues instead
measured brightness using photons
recorded in the unsaturated pixels
around the central one(s) and showed
that this halo is a reliable measure of
stellar brightness.

PLEIA DES G R A PHS: T. WHITE E T A L. / MONTHLY NOTICES OF THE R OYAL ASTR ONOMICAL SOCIE T Y 2017;
E XOPL A NE TS: ESO / M. KOR NMESSER

EXOPLANETS

Heavy Metals in Hot Jupiter
Atmosphere
RESEARCHERS HAVE found strong
evidence of titanium oxide (TiO) in the
atmosphere of hot Jupiter WASP-19b
- a Jupiter-mass planet with a surface
temperature of 2000K that orbits its
host star in only 19 hours.
Just as ozone absorbs solar radiation in Earth's atmosphere, creating an
inversion layer within which tempera-

Artist's impression of exoplanet WASP-19b

ture increases with altitude, titanium
oxide may play the same role in the
exotic atmospheres around hot Jupiters.
But while many astronomers suspect
TiO's presence, actually detecting this
molecule has proven difﬁcult.
As WASP-19b transited across the
face of its star, Elyar Sedaghati (European Southern Observatory) and
colleagues employed ESO's Very Large
Telescope (VLT) to capture the star's
light as it passed through a sliver of the
planet's atmosphere. The air absorbs
certain wavelengths depending on its
chemical makeup. Analyzing the light
captured by the VLT, the astronomers
found strong evidence for the presence
of titanium oxide in the atmosphere,
accompanied by water and sodium, as
well as a thick, light-scattering haze.
The results are published in the September 14th Nature.

The seven brightest stars of the Pleiades are blue-giant stars brighter and
more massive than the Sun, nearing the
end of their short lives. As expected for
this type of star, the new observations
reveal that they all pulsate, slowly varying in brightness by less than 1%. Their
light curves are shown at left.
Among them, Maia (20 Tauri) is
unusual. It has a slow rotation and
calm atmosphere, both of which allow
unusual concentrations of heavy elements to circulate near its surface.
Kepler observations reveal that Maia
varies over an exceptionally long period,
brightening and fading with a period of
10 days. The cause, the authors argue, is
most likely a large, chemically enriched
spot on its surface. If the spot is ﬁ xed,
then it probably has some relation to
the star's magnetic ﬁeld, but more data
are needed to learn how and why these
chemical spots exist.
■ MONICA YOUNG

IN BRIEF
7-Year Radio Survey
Begins Observations
The iconic antennas of the Karl G.
Jansky Very Large Array (VLA) have
started scanning the sky as part of a
new survey that promises the most
complete map of radio-emitting
celestial sources ever made. The VLA
Sky Survey (VLASS) will require seven
years of constant operation (a total of
5,500 observation hours) to cover 80%
of the Earth's sky from its location in
New Mexico's desert. It will scan the
sky three times, each scan separated
by about 32 months, which will enable
astronomers to watch sources evolve,
as well as to look for short-lived events.
Data will be made publicly available as
soon as they're acquired. Astronomers
expect that the survey will find around
10 million new objects - four times
more than currently known - including
new supernovae, neutron-star collisions, and supermassive black holes.
■ JAVIER BARBUZANO

■ JAVIER BARBUZANO
sk yandtelescope.com * JA N UA RY 2 018

http://www.skyandtelescope.com/

Sky and Telescope - January 2018

Table of Contents for the Digital Edition of Sky and Telescope - January 2018