- Williams and Toro Rosso unveil new cars at Jerez on Tuesday
- F1 teams are at the Spanish circuit for a four-day preseason test event
- Brazil's Bruno Senna will race for Williams, following in the footsteps of his uncle Ayrton
- Lotus' 2007 world champion Kimi Raikkonen led the way on the first day of testing
Williams and Toro Rosso both unveiled their cars for the 2012 Formula Season on Tuesday as the first official preseason testing event began at the Jerez circuit in Spain.
Williams, a legendary name in F1 with nine constructors' titles but none since 1997, hope the FW34 will help the UK-based team improve on a disappointing 2011 campaign which produced just five points in 19 races.
Williams recruited Brazilian Bruno Senna as a replacement for his veteran compatriot Rubens Barrichello, who is without an F1 seat for the first time since 1993.
Senna is following in the footsteps of his legendary uncle Ayrton, a three-time world champion who died following a crash at Imola in 1994 in his third race for Williams.
"I'm very excited to be back in action," the 28-year-old, who raced for Renault in the second half of last season, told the team's official website. "This is my ever first preseason testing program since I started in Formula One two years ago.
"I'm really motivated and looking forward to working hard and with everyone in the team. I hope we have a successful month testing and developing the car so we arrive in Melbourne as well prepared as possible."
Senna will be paired with Pastor Maldonado, the Venezuelan who scored only one point during his rookie F1 season in 2011. Maldonado posted the 11th-fastest lap at Jerez on the first of four test days.
"It feels great to be back with the team and to start putting some mileage on the FW34," said the 26-year-old. "The car felt good and the systems were all working well this morning.
"I like the feel of the new Renault engine as well. It's still too early to make any predictions, but we are pushing hard and working to understand the car better."
Toro Rosso hope to build on an encouraging 2011 haul of 41 points -- the Italy-based team's highest total in F1.
Australia's Daniel Ricciardo forms a new driver line-up with French rookie Jean-Eric Vergne, replacing Switzerland's Sebastien Buemi and Spaniard Jaime Alguersuari.
Ricciardo spent the second half of last season racing for Spanish team HRT, but failed to finish higher than 18th in any of his 11 grands prix. He drove for Toro Rosso on Tuesday and posted a lap of one minute 20.694 seconds -- the fifth-fastest time.
"It was great to experience taking a completely new car out of the garage," the 22-year-old said. "We had a very productive morning and made good progress with our program.
"Then in the afternoon, we did a couple of longer runs, but had to cut it short. I'm looking forward to another productive day tomorrow, because this car is very enjoyable to drive."
Vergne -- a Formula Three world champion two years ago -- drove Red Bull's 2010 championship-winning car at last November's young drivers' test event in Abu Dhabi.
"Last year, we finished eighth in the constructors' championship and clearly we want to do better than that this time," said team principal Franz Tost.
"It is far too early to make predictions, but looking at the work we have done over the winter, we must set ourselves the target of finishing sixth or at least seventh by the time we pack up in Brazil in November."
The returning Kimi Raikkonen led the field for Lotus at Jerez with a time of 1:19.670.
The 2007 world champion left the elite division of motorsport in 2009 and has since had spells in NASCAR and the World Rally Championship.
Force India's British driver Paul di Resta was second fastest on 1:19.772, with Mercedes' German pilot Niko Rosberg third.
Australian Mark Webber was on display for Red Bull -- with reigning champion Sebastian Vettel set for outings Thursday and Friday -- and posted the fourth-fastest time with a lap of 1:20.496.
The 2009 title winner Jenson Button could only manage eighth place for McLaren, with Ferrari's Brazilian Felipe Massa ninth.
Button's fellow Brit and the 2008 champion Lewis Hamilton will be in action for McLaren on Thursday and Friday, along with Ferrari's two-time title winner Fernando Alonso.