Wright et al 2008: Jupiter type exoplanet has same orbital period as host star activity cycle

Here is an important study of high relevance to our interest in the link between planetary orbits and solar activity.
H/T Gerry Pease:

The Astrophysical Journal, 683: L63–L66, 2008 August 10
THE JUPITER TWIN HD 154345b
J. T. Wright,  G. W. Marcy, R. P. Butler, S. S. Vogt, G. W. Henry, H. Isaacson, and A. W. Howard
Received 2008 January 8; accepted 2008 February 12; published 2008 July 23

ABSTRACT
We announce the discovery of a twin of Jupiter orbiting the slightly metal-poor ( ) nearby [Fe/H] p
0.1
( pc) G8 dwarf HD 154345. This planet has a minimum mass of 0.95M_jup and a 9.2 year, circular orbit
with radius 4.2 AU. There is currently little or no evidence for other planets in the system, but smaller or exterior
planets cannot yet be ruled out. We also detect a ∼ 9 year activity cycle in this star photometrically and in
chromospheric emission. We rule out activity cycles as the source of the radial velocity variations by comparison
with other cycling late G dwarfs.

Subject headings: planetary systems — techniques: radial velocities

3. ACTIVITY CYCLES IN LATE G DWARFS
We monitor all of our program stars for variations in
chromospheric activity, extracting Mount Wilson S-indices from
our RV science spectra (H. Isaacson, in preparation; Wright et
al. 2004). We have found that HD 154345 shows clear evidence
of a stellar cycle. Figure 2 shows that the magnetic activity
level of HD 154345 varies sinusoidally with a ∼ 9 year period.
Photometric monitoring from Fairborn Observatory (Henry
1999) confirms the presence of this activity cycle: Figure 3
shows a ∼ 1 mmag photometric variation in phase with the
chromospheric emission.

Deming et al. (1987) observed an apparent drift in line centroids
of CO transitions at 2.3 mm in the integrated solar spectrum
over a 3 year span. They associated these shifts with
changes in the activity level of the Sun over that period, and
suggested that activity cycles on Sun-like stars could thus
mimic the RV signature of a long-period exoplanet. The apparent
coincidence of the phase of HD 154345’s magnetic cycle
with that of the radial velocities in the same sense at the shifts
seen by Deming et al. (1987) therefore demands that we take
a closer look at the effects of stellar activity cycles on radial
velocities measured in the optical.

The Mount Wilson H and K activity survey (Baliunas et al.
1995) identified several stars of similar color to HD 154345
as exhibiting activity variations consistent with cycles.

We have
over 6 years of RV data at Keck for a total of four of these
stars: HD 26965, HD 3795, HD 10476, and HD 185144, the
latter three of which we have monitored regularly at Keck for
over 10 years

Based on these four stars, we conclude that long-term radial
velocity variations are generally not seen in the optical absorption
lines of late G stars undergoing magnetic activity cycles,
even cycles as strong as those in HD 185144. We note
that the Sun’s 11 year activity cycle has a period similar to
that of Jupiter’s orbit, and that the Mount Wilson survey
demonstrated that decadal activity cycles are a common feature of
old G stars (Baliunas et al. 1995). We thus consider the fact
that HD 154345 exhibits an activity cycle with a period and
phase similar to that of its Jupiter twin to be an inevitable
coincidence.

See  the full paper here

When Leif Svalgaard told us all on WUWT earlier this year that “ Unfortunately no effects of planets around other stars on stellar activity have yet been found. See the final slides of http://www.leif.org/research/AGU%20Fall%202011%20SH34B-08.pdf ” It seems this is another study he has missed, besides the one flagged up here a week or so ago. I’m sure that failing to be aware of this pertinent research is an unfortunate oversight on Leif’s part and that he will soon be correcting his errors by contacting the people at AGU 2011 he accidentally misled, as well as making an announcement at WUWT. 🙂

Following up the Balliunas reference, it turns out that observation of activity cycles on distant stars has been ongoing at Mount Wilson Observtory since 1966. I wonder which of these will be studied for planetary periodicities apart from the four noted by Wright et al.

The rest of the Donahue article is here.