New Planet Science to be Addressed by Next Generation Multi Object RV Planet Surveys

The next generation multi-object RV planet survey is becoming the most efficient way to detect and charcterize hundreds and even thousands of new giant planets in the next decade. Within each of the SDSS telescope FOVs, there are over one hundred candidate stars with V<12. A coupling of the multi-object DFDI instruments with the SDSS telescope will allow simultaneous monitoring of over 100 stars for planet detection and characterization with a moderate to high RV precision (about 10 m/s Doppler precision for a V— 11 solar-type star with a DFDI type instrument in an hour integration at the SDSS telescope). This kind of accuracy is sufficient to uncover most of the giant planets with a Jupiter mass and a year period since such a planet produces RV variations with a semi-amplitude of — 30 m/s on a solar-type star.

Below we use the MARVELS survey as an example to illustrate important planet science to be addressed by the next generation multi-object RV planet surveys.

The baseline MARVELS survey plan is to monitor a total of V - 8-12 10,000 MS and subgiant stars and 1,000 giant stars in 2008-2014 using two Keck ET instruments with 120 object capability with the precision and cadence needed to detect giant planets with orbital periods of a few days to —2 years in 2008-2014. The survey can be extended well beyond 2014 to detect and characterize additional long period planets.

The MARVELS survey has the capability to accommodate additional specialty instruments for exploring new planet parameter space, such as the low-mass star (mainly M dwarf) and super Earth mass planet regimes in 2008-2014. Figure 2.12 illustrates the parameter space that a full-scale MARVELS planet survey can cover in the next decade.

2.6.1 Giant Planet Science

The MARVELS optical survey with Keck-ET type instruments will be able to provide the comprehensive data set needed to characterize the population of giant planets with short and intermediate periods (e.g. P< 2 years), and to test theoretical models of the formation, migration, and dynamical evolution of giant planet systems. In detail:

- The MARVELS survey will explore a much larger range of the parameter space of stellar properties than any of the previous and current RV surveys as a single survey project. For instance, as shown in Fig. 2.12, stellar masses in the range 0.6-5 M© will be explored with the optical Keck ET type survey instruments (the 0.2-0.6 M© range can be explored with a red-sensitive survey instrument), while stars of a wide range of metallicity, activity level and age will be included in the target sample.

- The broad selection of target stars will make MARVELS ideal for studying the correlation of planet systems with stellar metallicity, mass, multiplicity, age, evolutionary stage, activity level, and rotation velocity.

Fig. 2.12. The planet mass (Y-axis) versus stellar mass (X-axis) showing the exploration space for the MARVELS planet survey. The filled circles are the known planets detected by the RV method, the open triangles are the known planets detected by the transit method. The grey region is probed by the Keck ET instruments, while the striped regions marked with RET and EXPERT, would be accessible to the red-sensitive and high-precision, optical RV instruments, respectively.

Fig. 2.12. The planet mass (Y-axis) versus stellar mass (X-axis) showing the exploration space for the MARVELS planet survey. The filled circles are the known planets detected by the RV method, the open triangles are the known planets detected by the transit method. The grey region is probed by the Keck ET instruments, while the striped regions marked with RET and EXPERT, would be accessible to the red-sensitive and high-precision, optical RV instruments, respectively.

- If planets around metal poor stars are detected by MARVELS, they will provide much stronger constraints on theoretical models of planet formation and evolution in metal-poor environments. Any detection of giant planets around stars with [Fe/H]<-0.5 would support the hybrid planet formation model for giant planets (i.e., giant planets form through disk instability in the metal poor disk environments (e.g., Boss 2002) vs. through core accretion in the metal-rich disk environment). On the other hand, a possible null detection of any giant planets around stars with [Fe/H]<-0.5 may place significant constraints on the disk instability model (Durisen et al. 2007).

- The detection of planets around giant stars will provide an important sample for a systematic study of planet formation and evolution around massive stars. The detection of new planets around active stars will offer the first significant sample of planets around these relatively young stars and allow direct comparison of their properties with the well established planet populations around older stars.

- A combination of the large number of new planets from a homogeneous survey sample with the survey efficiency calculations from the survey simulation models can be used to quantitatively test the planet distributions predicted by current planet formation models (i.e., Ida & Lin 2004a,b; Alibert 2005)

- The large number of short and intermediate period planet systems probed by MARVELS are the key to understanding the migration of giant planets after their formation. The semi-major axis distribution of short and intermediate period giant planets depends on the protoplanet disk conditions, the planet migration rate and the migration stopping mechanisms. Therefore, the measured distribution can test competing models for giant planet migration (Mordasini, private communication; Ida and Lin 2004a,b; Armitage 2007; Kornet et al. 2005; Ford & Rasio 2006; Wu et al. 2007)

- The large sample of planets will enable us to confirm or reject the marginal trends currently seen in the distributions of planet parameters with much higher confidence levels, such as the shortage of massive planets with 10-100 day periods, the planet mass fucntion at the high mass end (the "brown dwarf desert" region).

- The MARVELS optical survey will identify rare and interesting planetary systems for follow-up observations. These could include massive hot Jupiters, rapidly interacting multiple planet systems, very-hot Jupiters, and/or planets with extremely high eccentricities. Furthermore, stars with short period planets are also promising targets for longer term high-precision radial velocity monitoring to detect long period companions at large orbital separations and/or multiple planet systems. Multiple planet systems are particularly valuable for providing clues to the orbital evolution that shapes planetary systems.

- Transiting planets to be detected by the MARVELS survey will be important for detailed studies of planet properties. RV detected transiting planets are not biased toward the largest (radius) objects at fixed mass compared to those detected by transit surveys which are biased toward bloated and short-period planets (e.g., Gaudi 2006). These selection effects can be very difficult to quantify, particularly for ground-based transit surveys.

- MARVELS will be the best survey to date for exploring the "brown dwarf desert," the apparent paucity of ~ 15 — 80MJ companions to solar-type stars. MARVELS may discover new planetary systems with properties that have not previously been seen and have not been anticipated by theory.

2.6.2 Comparison with Other Planet Surveys

Compared to other on-going and planned RV searches using single-object spectro-graphs, MARVELS will monitor relatively faint stars, but many more of them. This survey target selection makes MARVELS especially powerful for detecting relatively short and intermediate period giant planets (P<2 years) with large velocity amplitudes. The MARVELS survey is complementary to transiting planet surveys which are sensitive to short period planets, but only those edge-on systems. The MARVELS survey is also complementary to microlensing planet searches (Bennett et al. 2007; Gould et al. 2007) and to space-based astrometric searches such as Space

Interferometry Mission (SIM) PlanetQuest and GAIA, which are more sensitive to longer period planet systems (several years or longer).

Ground-based transit surveys are primarily sensitive to Jupiter-sized planets orbiting bright stars, and are strongly biased toward planets with periods less than a few days. Space based transit surveys, such as Kepler, can detect relatively long period planets. However, the total detection number is very small because the transit probability declines as P-2/3. Based on the close-in giant planet frequencies derived by Gould et al. (2006), Kepler should find ~ 20 giant planets with periods between 5 days and two years, most of which will be detected around the V ~ 14 Kepler stars.

The proposed next-generation ground and spaced-based microlensing surveys (Bennett et al. 2007; Gould et al. 2007) are primarily sensitive to planets with separations of several AU and can only yield statistics for planets since the host stars of detected planets will generally be too distant and faint for follow-up.

SIM will primarily focus on a small number of stars 100) to detect terrestrial like planets. SIM has the best sensitivity in discovering planets at orbital distances close to its 5 year mission lifetime, considerably greater than those found by MARVELS.

GAIA will survey 100,000 V<12 MS stars comparable to MARVELS over its five-year mission lifetime and can potentially detect ~1,000 Jupiter-mass planets around these stars (Lattanzi et al. 2000, Sozzetti et al. 2005). Like SIM, GAIA's sensitivity will peak near orbital periods close to the mission lifetime, and so most of the detected planets will have several AU orbits.

Therfore, for the next decade, MARVELS will provide a unique large homogeneous sample of giant planets with orbital periods of a few days to over one year for characterizing giant planets and studying planet formation and dynamical evolution.

2.6.3 Super-Earth Mass Planets

One property of the MARVELS survey (common to all multi-object RV surveys) is that most of the fibers are devoted to faint stars which require longer exposure times and have limited Doppler precision. However, there will be a handful of bright stars in each field for which there is the opportunity to carry out an RV survey at much higher precision in both optical and red wavelengths. This simply requires building an instrument with higher resolution, and thus higher precision, based on the same multi-object DFDI technology. With additional high precision optical and red sensitive multi-object RV instruments, MARVELS can become a powerful tool for detecting a large number of super-Earth mass planets.

A large sample of super-Earth mass planets can help to address the frequency of super-Earth mass planets around nearby stars, what fraction of them are in the habitable zone, their mass and orbital parameter distribution such as semi-major axis and eccentricity, and their correlations with stellar properties of their host stars. Furthermore, a larger sample of these planets will lead to the detection of possible transiting planets, which will be used to determine the typical planet density and mass-radius relation, to test the idea that these are indeed rocky planets.

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