How old are stars?
Astronomers have developed a new method for accurately determining the ages of field stars based on their rotational rates.
Provided by the Lowell Observatory
"Gyrochronology transforms a rotating star into a clock which is set using the Sun
and keeps time well," says Sydney Barnes, Lowell Observatory astronomer.
NASA / SOHO
April 26, 2007
Gyrochronology, a new method for accurately determining the ages of field stars based on their rotational rates, is being announced today by Sydney Barnes, Lowell Observatory astronomer. This fundamental research, "Ages for illustrative field stars using gyrochronology: viability, limitations and errors," is accepted for publication in an upcoming issue of the Astrophysical Journal.
The age of a star is its most fundamental attribute apart from its mass. A star's age tells astronomers how astrophysical phenomena change over time. "For example, the ages of the host stars of planetary systems are needed to understand how these systems change over time," says Barnes.
By showing that the rotation period of a star is a steadily changing and tight function of its age and color, gyrochronology allows the age to be determined by measuring the two other properties — the rotation period and the color. "If you know the relationship between three quantities, measuring two of them allows you to calculate the third," says Barnes. "The relationship between age, color, and rotation period has particular and useful mathematical properties that simplify the analysis and allow the uncertainties to be calculated easily." A star's color is a proxy for its mass or surface temperature. The uncertainties in gyrochronology ages are typically 15 percent; with preexisting stellar aging methods the uncertainties range from 50 to 100 percent.
Gyrochronology can be calibrated using the known age of the Sun (4.6 billion years). Another distinguishing characteristic of the technique is that it works well for the vast majority of stars including field stars, or those not found in star clusters. For the first time, this new technique makes possible the derivation of accurate ages for solar- and late-type main sequence stars using only their rotation periods and colors. In his new paper, Barnes calculates ages for sun-like and other low mass stars that burn their hydrogen fuel at a relatively steady rate on what is known as the main sequence. Barnes derives ages for sample stars where rotation and color are known, but the stellar ages using other methods are not known.
The technique builds on an insight of Skumanich in 1972 who noticed that another measure of stellar rotation changes steadily with the ages of star clusters. However, the related imprecision greatly compromises the accuracy of ages derived using this insight alone. Measurements made at Lowell Observatory in the late 1980s showed that rotation also depends on the color/mass of a star. Gyrochronology combines and develops these two insights into a precise way of deriving stellar ages, and shows that it works even for single field stars. The paper shows that the rotation period of a star (whether in a cluster or in the field) can be written as a simple product of two separable functions of its age and color. This mathematical behavior provides the key simplification that makes gyrochronology unique.
Full article
http://www.astronomy.com/asy/default.aspx?c=a&id=5479
Astronomers have developed a new method for accurately determining the ages of field stars based on their rotational rates.
Provided by the Lowell Observatory
"Gyrochronology transforms a rotating star into a clock which is set using the Sun
and keeps time well," says Sydney Barnes, Lowell Observatory astronomer.
NASA / SOHO
April 26, 2007
Gyrochronology, a new method for accurately determining the ages of field stars based on their rotational rates, is being announced today by Sydney Barnes, Lowell Observatory astronomer. This fundamental research, "Ages for illustrative field stars using gyrochronology: viability, limitations and errors," is accepted for publication in an upcoming issue of the Astrophysical Journal.
The age of a star is its most fundamental attribute apart from its mass. A star's age tells astronomers how astrophysical phenomena change over time. "For example, the ages of the host stars of planetary systems are needed to understand how these systems change over time," says Barnes.
By showing that the rotation period of a star is a steadily changing and tight function of its age and color, gyrochronology allows the age to be determined by measuring the two other properties — the rotation period and the color. "If you know the relationship between three quantities, measuring two of them allows you to calculate the third," says Barnes. "The relationship between age, color, and rotation period has particular and useful mathematical properties that simplify the analysis and allow the uncertainties to be calculated easily." A star's color is a proxy for its mass or surface temperature. The uncertainties in gyrochronology ages are typically 15 percent; with preexisting stellar aging methods the uncertainties range from 50 to 100 percent.
Gyrochronology can be calibrated using the known age of the Sun (4.6 billion years). Another distinguishing characteristic of the technique is that it works well for the vast majority of stars including field stars, or those not found in star clusters. For the first time, this new technique makes possible the derivation of accurate ages for solar- and late-type main sequence stars using only their rotation periods and colors. In his new paper, Barnes calculates ages for sun-like and other low mass stars that burn their hydrogen fuel at a relatively steady rate on what is known as the main sequence. Barnes derives ages for sample stars where rotation and color are known, but the stellar ages using other methods are not known.
The technique builds on an insight of Skumanich in 1972 who noticed that another measure of stellar rotation changes steadily with the ages of star clusters. However, the related imprecision greatly compromises the accuracy of ages derived using this insight alone. Measurements made at Lowell Observatory in the late 1980s showed that rotation also depends on the color/mass of a star. Gyrochronology combines and develops these two insights into a precise way of deriving stellar ages, and shows that it works even for single field stars. The paper shows that the rotation period of a star (whether in a cluster or in the field) can be written as a simple product of two separable functions of its age and color. This mathematical behavior provides the key simplification that makes gyrochronology unique.
Full article
http://www.astronomy.com/asy/default.aspx?c=a&id=5479