Sunday 27 May 2018

#VLTJupiter 6: A Tour of Cerro Paranal

The first glimpse of the VLT came as our bus arrived at the Residencia from Antofagasta.  Four gleaming silver boxes on top of a flattened mountain.  We couldn't wait to get up there to see inside, so took the "Star Trail" path up to the summit on our second day.  This dusty path took around an hour, looping around to the west of the mountain to give us good views of the Pacific Ocean, albeit obscured by clouds held near the ground by an inversion layer.  The first thing you come to is the control building, over three stories high but beneath the main level.  This is where the astronomers sit, night after night, with control panels for each of the Unit Telescopes (UTs).  Take a gantry staircase up to the top, and you arrive at one of the most sophisticated and awe-inspiring telescope sites in the world.

Credit:  Iztok Boncina/ESO

The Telescopes

A map of the Paranal site, from the Residencia up to the VLT platform.

The four UTs, Antu, Kueyen, Melipal, and Yepun, each stand over 28.5 m high, each containing the 22-tonne 8.2-m diameter primary mirrors - single, monolithic mirrors, as large as we can build them with our technology today, made from a special glass-ceramic with almost no thermal expansion, called Zerodur.  These are mountain on a 350-tonne alt-azimuth mount, with a 1.1-m diameter beryllium secondary mirror to reflect the light back to the instruments at the Cassegrain focus.   Active optics with 150 supports control the shape of the thin (177 mm thick) primary mirror.  We got to go inside UT3 just as the sun was setting, and seeing this huge structure moving and rotating with very little sound was quite incredible.  We stood in total darkness, until suddenly the huge dome doors opened up, letting the moonlight flood in.  The wind shields behind the dome doors then opened one by one, as well as the vents all around and below the telescope - this lets the air in to keep the optics down at the ambient temperature of the mountaintop.  The dome rotates silently to align with the chosen target, and the alt-azimuth mount slews to the right elevation.  This is astronomy on an industrial scale.

Watching these huge UTs move around was an absolute privilege, especially with the golden glow of sunset in the background, Venus setting, and Jupiter rising in the east.  By the time we'd finish each night, Saturn was also high up in the sky.

The four UTs aren't the only things up on the platform - there are four additional 1.8-m telescopes called the ATs (auxiliary telescopes).  These are dedicated to full time interferometry, being able to move the ATs around on rails to produce a variety of different baselines (the further apart they are, the finer the scales they probe).  The UTs can also be used for interferometry, increasing the light collecting power, but it means that they're all being used at the same time on the same object, and no one else can use the instruments.  The beams from each telescope are combined in "delay lines" beneath the platform, where they are fed into different instruments.

ESO/H.H. Heyer

Happy Birthday

While we've been here at Paranal, UT1 celebrated a very special anniversary - it achieved first light exactly 20 years ago, on May 25th 1998, and in excess of 330 million EUR were spent in ESO Member States for the construction of the VLT.  The other UTs followed:

UT2, Kueyen: 1 March 1999
UT3, Melipal: 26 Jan 2000
UT4, Yepun: 4 September 2000

The annual budget is 16.9 million EUR without personnel costs, You can see recent 360-degree images of the summit here, and take a virtual tour here.  This website showing the current conditions is extremely useful.

"There's no cause for alarm.... but there probably will be."

Saturday 26 May 2018

#VLTJupiter 5: A Tour of the Southern Sky

One of the incredible things about being on top of Cerro Paranal is the stunning visibility of the night sky and the Milky Way.  And for someone born and raised in the northern hemisphere, things can look decidedly odd.  The first thing that you notice is the moon, with the typical distribution of Mare and craters appearing upside down as viewed from the southern hemisphere.  Orion, typically a winter constellation for us, is visible at sunset from Chile.  But it's tipped over on its side, like a drunken archer, falling into the Pacific Ocean, Betelgeuse first.

Credit: ESO/Y. Beletsky

Our supporting astronomer, Florian, took us outside to see the night sky, standing in the shadow of UT1.  He pointed out Alpha Centauri 4.37 light-years away, and made the excellent point that our Sun would look exactly the same if we were standing on a planet orbiting that star, towards the constellation Cassiopeia.  Just above this bright star is the Southern Cross, although I didn't spot it at first - I was expecting five stars in a cross shape, but it's actually four stars in a kite shape.  The long axis of the Southern Cross points then towards the southern celestial pole - no pole star there, like there is in the northern hemisphere.  Just below the Cross was a darker region of the Milky Way - this was the Coalsack Nebula, 600 light years away, and blocking out the light from the galaxy.

Bruno Gilli/ESO -

Looking to the southwest, we could see Sirius and Canopus (second brightest star in the sky after Sirius), and using 1.5x the distance between them, following the line south, I say a breathtaking sight - my first ever view of the Large Magellanic Cloud (a dwarf galaxy orbiting the Milky Way), as a fuzzy blob south of the main band of the Milky Way.  I never knew these could be seen with the naked eye, they're quite the sight!

A lot of the objects can be identified using the website.

#VLTJupiter 4: Observing with VLT

Observing from a large telescope is a rather different experience to what you might imagine.  It's not a case of being outside with the equipment, your eye to the eyepiece, capturing your data.  We're sat in a control room several floors below the VLT platform, with UT3 doing its work remotely on the mountain top.  In fact, all the telescopes are controlled from here - there are horseshoe-shaped desks for each telescope (the UTs), each one with a telescope operator, the support astronomers and, in our case, space for the visiting astronomers.  There's also space for the ELT (which will be controlled from here, even though its platform, Cerro Armazones, is kilometres away) and the interferometry.  It’s all very high-tech, but essentially a large open plan office where the astromers sit for the full night.

We have dinner in the Residencia at around 5pm, then drive the 10 minutes up the mountain in ESO's fleet of old, slow Fiat Puntos.  Sunset happens pretty fast at this latitude of 24S, so we head up to the VLT platform to watch the sun vanish over the Pacific ocean, shrouded in an array of brightly coloured clouds.  In fact, the clouds always obscure the ocean itself, hiding it beneath an unending mat of white.  To the east, deep purples and pinks show the shadow of the mountain, with Jupiter rising (we're really close to opposition right now).  Venus has been glowing bright as the Sun disappears, but there's little time to waste as we head back down to the control room.

VISIR Observation Strategy

Padraig and I have had a plan each night for the sequence of VISIR 5-20 µm observations, with the ultimate aim of using Jupiter's ten-hour rotation to map out as many longitudes as possible, generating full maps of the planet in lots of different spectral settings.  The benefit of mid-infrared observing is that we don’t need to wait until it gets dark to start taking data - the sky is always bright in the mid-IR.  We can start during twilight, which ends around an hour after sunset.  The telescope operator, Ben, would find a nearby bright star to guide on and to perform the "active correction" - deforming the main 8.2-m mirror with a series of actuators to correct for distortions caused by flexure and temperature changes.  Then our support astronomer, Florian, would load up the first of our observation blocks for execution.  These start with an acquisition template, a first glimpse of Jupiter so that we can move the telescope around a little, centring Jupiter, before starting the main observations.

Then it's a case of clicking go, and watching along as VISIR changes its filters and moves through the spectrum.  We have to get the timing right, as Jupiter's 10-hour rotation is surprisingly fast when you're running against the clock.  Sometimes we’ll break and do 20 minutes of "lucky imaging" (taking a video of the scene at 5 µm so I can then stack together only the sharpest frames, freezing the seeing), or 20 minutes of spectroscopy using VISIR's low-resolution mode.  These tend to need the most user intervention, but for the rest of the time it's a matter of making sure that nothing is going wrong as the images are acquired.

Staying Awake

There's been some moments of excitement.  On our first night, we were taking data at exactly the same time as Juno was executing its close flyby.  That meant that we caught the flyby longitude (29W) perfectly, about 45 minutes before Juno flew over it on the terminator.  We spotted that Juno flew over one of the 5-micron hotspots on the North Equatorial Belt, the first time that's been accomplished during the mission.  We also had several opportunities to view the Great Red Spot in all its glory - the GRS is really unusual at the moment, after the passage of the South Tropical Disturbance.  It looks like a spoon holding an egg.  And the southern aurora was really vivid in all of our images (not so the northern aurora).  These all brought gasps from the other astronomers in the room - I don't think any of them are used to being able to see such incredible data in the raw images.

Glenn and colleagues were also observing on Subaru for two of the nights, so at one point we had a live Skype conversation going as VISIR finished its Jupiter observations and COMICS picked them up from Hawaii - two of the world's best observatories working in tandem.  We also had the Oxford service mode run on MUSE operating one night, so both UT3 and UT4 were looking in the same direction.

But there were some bad moments too.  To get decent images of Jupiter we really want to be chopping the telescope by more than 45 arcseconds, but we've always been limited to 25 arcsec in the past.  We tried to be cheeky and push this to 30 for some observations, which worked on the first night, but on subsequent nights it caused severe upsets.  The M2 mirror lost all power and had to be rebooted - literally turning it off and on again to get it working, which meant we lost 30-60 minutes of time on the second night.  Furthermore, the spectroscopy and burst mode imaging with VISIR proved to be exceedingly difficult.  I spent most of my daytime hours trying to figure out the complexities of their reduction, coming back to the mountain the next night with suggestions for improvements.  On the plus side, we'd be experts in VISIR data acquisition by the end of the run….

The first couple of nights spoiled us with excellent conditions - low wind, perfect seeing, incredibly low water vapour.  Heading up on the mountain on the third night, we could see light cirrus overhead and the temperature had dropped.  We were going all-guns-blazing until around 21:30, when the wind went above 12 m/s, meaning that we had a 'pointing restriction' and had to turn the telescope away from Jupiter.  Above 18 m/s and they have to close, so we remained open, but executing service mode observations pointing away from the wind direction out of the north.  I can’t tell you how frustrating it is to sit watching the minutes (and Jupiter longitudes) flick by while we can’t observe…  but on the plus side, the support astronomers were generous.  When the wind dropped at about 1am, they gave us the extra few hours back, and we continued with Jupiter until around 4am in the morning.

Night's End

At the end of each half-night we'd hand back over to the interferometry mode, which uses all four Uts.  We'd collect our things and head outside to the Puntos, but it was astonishingly dark outside when the moon had set, providing us with a stunning view of the night sky, the Milky Way, and the Magellanic Clouds.  Almost enough to want to stay up longer, until sleep deprivation took its hold…

#VLTJupiter 3: ESO's Residencia

One of the most incredible things about this whole experience has been staying in the Residencia, about 300 m below the mountain peak in the middle of the desert.  This award-winning hotel has been in use since 2002, and will likely be expanded in the future to accommodate all the new users of ELT.  In fact, it was designed to be part of the landscape rather than to obscure it, being built below ground with only the south-facing windows and doors being visible.  From the outside, it's a long red-brown structure that blends in with the surrounding red-brown hills, with a white dome over the roof.  When the bus first pulls up, you end up going down a long ramp to a pair of thick, grey doors.  As soon as you open them, though, the arid desert vanished and you enter the tropics, at the top of a long spiralling ramp that takes you down to the reception desk.

The south facing rooms of the Residencia.

In the centre of this curved walkway is a tropical oasis, with palm trees, colourful flowers, and even birds flying from plant to plant.  Right in the middle is a swimming pool, which I haven't seen used at all during my stay, but which I'm told is there to help the humidity of the building.  Nearby are comfy chairs, a table-tennis table, and table football.  For the musically inclined, there's a fully stocked music room next to a cinema/library room.   A row of offices for visiting astronomers looks out over the pool (I spent several hours sat in those offices getting work done during the day).

The rooms themselves are along a long, elongated stretch of building, with ramps rather than stairs running between floors.  My room faced south, with a door that you could open onto the silence of the desert.  In fact, apart from the footsteps of the odd passing astronomer, it was so silent in the Residencia - bliss when trying to work or get some sleep.  Food is served almost constantly in the canteen, which you scan in and out of - you could get very fat here, with so much on offer.  They even ship food up to the control room at night, so we dined on pizza and cake in the small hours of the morning, washed down with coffee to keep us awake.

The pool and reception area.  Credit:  P. Horálek/ESO

My interest in this building goes beyond just the gorgeous architecture.  I'm a huge James Bond fan, so it's wonderful to be staying in the "Perla de las Dunes", a "Bolivian" hotel and lair of the bad guy in Quantum of Solace.  That version was blown up by Bond in his climatic battle (in Pinewood, at least), but the exterior shots were all filmed here.  Lovely connection between my two loves - Bond and planetary science!  And being visitor number "007" was also quite a perk.

But back to astronomy  - on our first couple of evenings here, it was hard not to spend time outside gazing up at the night sky.  We'd go and sit in the shadow of UT5, the small public telescope near the hotel, blocking out the moonlight.  Again, the silence was perfect, and the stars spectacular.

Wednesday 23 May 2018

#VLTJupiter 2: Journey to Paranal

Chaotic.  That's probably the best way to describe my second-ever trip to South America.  We were late boarding the flight from Heathrow having gotten confused between A and C terminals and having to run through the tunnels beneath the runway.  We were almost late boarding the flight from Madrid because the "transfer" signs weren't obvious and we ended going through the immigration counters twice.  And arrival in Santiago, at around 7.30am, was a nonsense - no idea where to collect baggage, enormous immigration queues, and even larger customs queues.  It took us a good couple of hours to escape the airport, find the TransVIP desk and get our cab out to the ESO Guest House in Las Condas, on the east side of Santiago.

Some of this was ameliorated by a very comfortable, modern airliner with LATAM - no window shades, but buttons used to change the opacity of the windows themselves!  And the view over the Andes at sunrise, as we came into land, was nothing short of spectacular:

I'm travelling with my 2nd-year PhD student, Padraig Donnelly, whose job it'll be to analyse the Jupiter data we acquire from the VLT.  We'll get to that, but for now, we had a whole Sunday to explore the beautiful city of Santiago.  The taxi to the guesthouse cruised along modern, broad freeways into a residential district west of Santiago, and we were immediately struck by the autumnal look of the place - orange and red leaves on the trees, quite the contrast to the springtime Britain that we'd left behind.  The guesthouse was a very laid-back affair:  three low-level wings of bedrooms, surrounding a central courtyard and fountain, with an unused swimming pool out the back.  There was a lounge with coffee machines, books, and a stereo, and a dining room where breakfast, lunch and dinner were served by the very friendly staff.

Exploring Santiago

After breakfast and a shower, we walked 15 minutes to the Escuela Militar underground station, purchasing a "BIP" card with enough credit for a return trip (about $3000 pesos) and travelling to Santa Lucia station.  From there we took a walking tour of the Centro district, half-remembered from the last time I visited Santiago in 2015.   We climbed the Santa Lucia hill, a landscaped region of gardens and statues, to reach the red-brick Torre Mirador at the summit, with its excellent panoramic views of the city and the Andes in the distance.  We found our way to the Mercado Central fish market, dined in the central "Agusto" restaurant on Sea Bass and prawns, fresh from the market stalls, and then wandered the shopping streets of the Centro district to do some people-watching near the Plaza de Armas and Catedral Metropolitana, right in the heart of the city.   Other than tourists, it was notable how peaceful the city was - almost all of the shops and businesses were closed, and it was great to see a country respecting Sunday as a day off work!

We returned to the Guesthouse via a bar near Escuela Militar, then wandered back in time for Pisco Sours at 18:45 (a time so regular that it was advertised on the wall of the guesthouse, next to the meal times).  We had a delicious 3-course meal in the dining room, meeting three other astronomers - two that had just returned from La Silla, and one who was about to travel to that observatory for the first time, and was excited as Padraig and I.

To Antofagasta!

Monday morning started at 5am, with a quick breakfast and shower, a taxi back to the airport, and an 8am flight north to Antofagasta.  This city, right on the Pacific coast and next to the Tropic of Capricorn at 23S, was previously part of Bolivia until the War of the Pacific in 1879-83, after which it was transferred to Chile.  In fact, we later discovered that today (May 21st) was "Navy Day", a national holiday in Chile, which explained why the city was quiet.  The landscape was dry and arid, as befitting a city in the Atacama desert, the driest place on Earth. An air-conditioned ESO coach picked us up at the airport and drove us into the city along the sea front, past the infrastructure of the port and the copper mining on which the economy was founded.   There we collected a few more people, and headed south into the desert and the mountains, along a smooth paved road through a desolate and dry landscape.  It was hard to escape the feeling that breaking down out here would be a VERY bad idea.

The coach continued south for a couple of hours, with very limited signs of any civilisation along the way.  Mountains were on either side of us, but the road followed a broad valley between them, before we branched off to the west and back towards the ocean.  The road climbed higher, along various switchbacks, until we finally caught a glimpse of what we'd been waiting for - in the distance, the gleam of four silver monsters sat upon the top of Cerro Paranal, the 2635-m high home to ESO's Very Large Telescope.  We stopped at the security lodge to collect our Visiting Astronomers badges, before descending into a tunnel under the desert soil - the entrance to ESO's astonishing Residencia building. 

Tuesday 22 May 2018

#VLTJupiter 1: Jupiter from the VLT

Over the past decade, I've been exceedingly fortunate to have won time on the European Southern Observatory's (ESO) Very Large Telescope (VLT) to observe all four of the giant planets in the mid-infrared.  These observations, sampling thermal emission from 5 microns in the M band, to 10 microns in the N band, and 20 microns in the Q band, can reveal the three-dimensional temperatures, winds, gaseous composition and cloud structure, from the churning, convective tropospheres all the way into their stable stratospheres.  Many of my papers and projects have relied on this exquisite VLT dataset.

But despite all of that, I've never been able to visit VLT in person.  It's been an item on my bucket list for over ten years.  My observations were always in 'service mode', meaning that I'd design them in a piece of software (i.e., which filters to use, where to point, and for how long), then upload them to the ESO office to be put into a queue.  Those queued observations are then executed by supporting astronomers on the mountaintop, in between time-critical 'visitor mode' runs.  The trouble with this approach is that it's been hard to control the exact timing of the observations, and the data were usually taken within 1-4 weeks of when I actually wanted them.  For most datasets, that's been absolutely fine.  But now that the Juno spacecraft is in orbit around Jupiter, completing close flybys of the gas giant once every 53 days, the precise timing of my observations has become more critical.  So today (May 22), I'm writing this blog post from 2300m up on Cerro Paranal in the astronomer's residence, waiting to begin a visitor-mode run tomorrow night.

A map of the ESO sites in Chile - we flew from Santiago to Antofagasta, before a bus journey south along the B-710 to Cerro Paranal.  Cerro Armazones, the future home of the ELT, can be seen as a flattened mountain in the distance to our east.

The Juno Connection

The Leicester team are a part of an international network of planetary astronomers supporting NASA's Juno spacecraft in its exploration of Jupiter.  Juno has now completed twelve close passes around Jupiter known as perijoves, coming in over the north pole, sweeping within a few thousand kilometres of the equator, then exiting high over the south pole.   The thirteenth such encounter is on May 24th at 05:40UT, approximately 48 hours from now.  Now, Juno has been doing some tremendous science, but its science questions are focussed, and there are gaps in capability within the payload.  The Earth-based programme has been providing support in three broad areas:

  1. Spatial context:  Juno has a close-in view of dynamic phenomena and weather systems as it flys north-south across Jupiter, and can't always see the wider context of the zone or belt in which that weather system is embedded.  In contrast, our data can view the whole planet at once, providing the global perspective.
  2. Temporal context:  Jupiter's weather and auroral processes can evolve significantly between the perijoves, with new storms erupting, vortices interacting, belts fading and expanding, and aurora shifting and changing in response to a variety of processes in the magnetosphere and solar wind.  The Earth-based programme catalogs these changes over short timescales (between perijoves) and long timescales (multiple years) to better interpret Juno's observations.
  3. Spectral context:  Juno does a fabulous job in the ultraviolet, visible (with imaging), 2-5 µm region (with imaging and spectroscopy) and 1.3-50 cm microwave region.  But there's nothing in the X-ray, 0.9-2 µm infrared, 5-25 µm thermal infrared, and the sub-centimetre range below 1.3 cm.  An army of Earth-based facilities, including Chandra, Hubble, VLT, Subaru, IRTF, VLA and ALMA, have been used over the past two years to plug this gap.  That's not to mention the amateur astronomers observing on a nightly basis.

Back in 2015, several representatives of these telescopes travelled to the ESO headquarters in Vitacura, near Santiago, for a week-long workshop on collaborations between ground-based astronomers and space missions.  I wrote about that meeting here.  As a result of this workshop, I led a white paper, addressed to the ESO Director of Science, that emphasised the timely nature of VLT and ALMA observations during the Juno mission, making the three points outlined above.  I like to think that they helped to smooth the way for the ESO proposals that ensued over the following three years, during which time we've been successful in winning service mode runs for Jupiter every semester.  These data will be useful for the Juno mission, but also for my work studying the long-term evolution of Jupiter's meteorology and climate.

And that brings me full circle to this silent mountaintop in northern Chile.  While we're working up here, I'm going to try to keep a record (who know's whether I'll ever have the chance to return!), to give a flavour of what it's like.  And that starts with the journey.

Current location - 12 km from the sea, 2.3 km in the air, on top of Cerro Paranal.  Cerro Armazones is off to our east.