Orbital Motion of Alpha Ursae Minoris from Radial Velocities.

Roemer, Elizabeth

doi:10.1086/148230

Cited by 21 publications

(22 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The values based on the radial velocity data sum-O Ϫ C marized by Roemer (1965) are illustrated in Figure 3, where the data are taken from the first 53 lines of Table 1. It should be clear from Figure 3 that the period variations in Polaris during the interval 1896-1958 are described very closely by a regular period increase of s yr Ϫ1 , as indicated 4.48 ‫ע‬ 0.06 by the close-fitting, positively sloped parabolic curve that matches the observations.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

The Period Changes of Polaris

Turner

Savoy

Derrah

et al. 2005

PUBL ASTRON SOC PAC

View full text Add to dashboard Cite

ABSTRACT. The evolutionary changes in pulsation period for the Cepheid Polaris are reinvestigated using archival observational material (radial velocities, photometry, and eye observations) over the interval 1844 to the present, including new photometry for the star obtained in [2003][2004]. The star's pulsation period increased at a rate of 4.5 s yr Ϫ1 during that interval, with the exception of a brief hiatus between 1963 and 1966, when it suddenly decreased, possibly as a result of a brief reduction in average stellar radius amounting to Ϫ0.055%. At roughly the same time, the pulsation amplitude of Polaris underwent a marked change. Prior to 1963 the V amplitude was in excess of about 0.1 mag, possibly decreasing at a rate of 0.019 mag century Ϫ1 . Following the hiatus of 1963-1966, the pulsation amplitude underwent a sharp decline and now appears to be erratic on a cycle-to-cycle basis, always smaller than 0.05 mag. The rapid rate of period increase for Polaris is consistent with a first crossing of the Cepheid instability strip, while the hiatus of 1963-1966 and sudden decrease in pulsation amplitude thereafter suggest that the star may have left the instability strip for first crossers at that time, leaving it near the center of the instability strip for Cepheids in higher crossing modes.

show abstract

Section: Resultsmentioning

confidence: 99%

“…Such a change might occur, for Roemer (1965). The fitted parabolic relation corresponds to a period increase of s yr…”

mentioning

confidence: 95%

The Period Changes of Polaris

Turner

Savoy

Derrah

et al. 2005

PUBL ASTRON SOC PAC

View full text Add to dashboard Cite

show abstract

“…This period increase has also been accompanied by a decrease in the pulsational amplitude. In 1896È1950 the peak-to-peak (2K) amplitude was D5È6 km s~1 (Campbell 1899 ;Roemer 1965), whereas by 1983 the amplitude had decreased to 2K \ 2È3 km s~1 (Arellano Ferro 1983 ;Kamper, Evans, & Lyons 1984). More recently D89 conÐrmed this decline in the amplitude by measuring an amplitude 2K \ 1.5^0.08 km s~1 during the year 1989.…”

Section: Introductionmentioning

confidence: 99%

The Radial Velocity and Spectral Line Bisector Variability of Polaris

Hatzes

Cochran

2000

The Astronomical Journal

View full text Add to dashboard Cite

We present precise stellar radial velocity measurements for the Cepheid-type star Polaris taken in 1992È1993. The peak-to-peak amplitude of the pulsations was 1.555^0.056 km s~1 in epoch 1992.4 and 1.517^0.047 km s~1 in epoch 1993.2. These amplitudes are comparable to the one measured by Dinshaw et al. in 1987.75 and Mg I j5528 lines also show variations with the 40 day period, strongly indicating that this period is indeed real. The presence of line bisector variations excludes a low-mass companion object as a cause of the residual radial velocity variations. Two models are considered for the residual radial velocity and bisector span variations : starspots and nonradial pulsations. Although both can reproduce the amplitude and shape of the residual radial velocity variations, the spot models considered were unable to reproduce the overall shape and amplitude of the bisector span variations. The best-Ðt spot model was provided by a single spot with a temperature 500 K cooler than the photosphere with a macroturbulent velocity of zero in the spot. If surface features do exist on Polaris and are responsible for the residual radial variations for this star, then possibly they have a temperature structure and distribution more complicated than the simple models considered here. The best Ðt to all the observed variations was provided by a nonradial m \ 4 mode, although these were not entirely satisfactory having a phase shift of about 0.25 between the observed and predicted bisector variations. Possible explanations for this shift include temperature e †ects, a source function originating in a dynamic stellar atmosphere, or a di †erent pulsation mode than the one that was considered. Although the exact pulsational mode is yet to be identiÐed, we believe that the residual radial velocity variations are due to a long-period pulsation mode. Supporting evidence comes from the fact that three di †erent residual variations with periods near 40 days have now been seen in Polaris and it is unlikely that these variations are due to rotational modulation by surface features on a star that is di †erentially rotating.

show abstract

“…The field surrounding Polaris appears to coincide with the remains of a poorly-populated star cluster. For example, the radial velocities of Polaris and its brightest companions are nearly identical: −16 km s −1 (Polaris, Roemer 1965;Kamper 1996;Turner et al 2006c Kamper 1996;Usenko & Klochkova 2008), and −11 km s −1 (HD 5914, Abt & Biggs 1972). A color-magnitude diagram for possible cluster stars from Hipparcos photometry is shown in Fig.…”

Section: The Polaris Clustermentioning

confidence: 99%

Polaris and its Kin

Turner¹

2009

AIP Conference Proceedings

View full text Add to dashboard Cite

A review is presented of the past 165 years of observation of the 4-day Cepheid Polaris, including the exciting results of the last 50 years, an interval that has produced three orbital solutions for the spectroscopic binary subsystem, recently resolved by HST, parameters for the optical companion, precise measurement of the star's trigonometric parallax and angular diameter, evidence for a rapid increase in its pulsation period, and observations of the dramatic decline and recent partial recovery of its light amplitude. There has been considerable discussion about the exact nature of the star, with potential resolutions summarized here. It is also noted that many of the star's characteristics are shared by a small number of other Cepheids that display rapid period increases identical to those predicted for stars in the first crossing of the instability strip, small light amplitudes, and intrinsic colors typical of variables lying near the center of the strip, where Cepheids of largest amplitude reside. While all members of the group appear to display the canonical traits of first crossers of the instability strip, Polaris has one unique peculiarity: a brief hiatus in its monotonic period increment between 1963 and 1966 during which the pulsation period underwent a dramatic decrease. Has the average brightness of the Cepheid also increased over the last millennium?Comment: Review given at the "Stellar Pulsation: Challenges for Theory and Observation" conference in Santa Fe, New Mexico (2009

show abstract

Orbital Motion of Alpha Ursae Minoris from Radial Velocities.

Cited by 21 publications

References 0 publications

The Period Changes of Polaris

The Period Changes of Polaris

The Radial Velocity and Spectral Line Bisector Variability of Polaris

Polaris and its Kin

Contact Info

Product

Resources

About