Kepler-37 is a G-type main-sequence star located in the constellation Lyra 215.2 light years from Earth.
 It is host to exoplanets Kepler-37b, Kepler-37c, Kepler-37d and Kepler-37e, all of which orbit very close to it.
 Kepler-37 has a mass about 80.3 percent of the Sun's and a radius about 77 percent as large.
 It has a temperature similar to that of the Sun, but a bit cooler at 5,417 K.
 It has about half the metallicity of our Sun.
 With an age of roughly 6 billion years, it is slightly older than the Sun, but is still a main-sequence star.
 Until January 2015, Kepler-37 was the smallest star to be measured via asteroseismology.
A blue straggler is a main-sequence star in an open or globular cluster that is more luminous and bluer than stars at the main-sequence turn-off point for the cluster.
 Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3.
 Standard theories of stellar evolution hold that the position of a star on the Hertzsprung–Russell diagram should be determined almost entirely by the initial mass of the star and its age.
 In a cluster, stars all formed at approximately the same time, and thus in an H–R diagram for a cluster, all stars should lie along a clearly defined curve set by the age of the cluster, with the positions of individual stars on that curve determined solely by their initial mass.
 With masses two to three times that of the rest of the main-sequence cluster stars, blue stragglers seem to be exceptions to this rule.
 The resolution of this problem is likely related to interactions between two or more stars in the dense confines of the clusters in which blue stragglers are found.
A G-type main-sequence star (Spectral type: G-V), often (and imprecisely) called a yellow dwarf, or G dwarf star, is a main-sequence star (luminosity class V) of spectral type G.
 Such a star has about 0.84 to 1.15 solar masses and surface temperature of between 5,300 and 6,000 K.
 Like other main-sequence stars, a G-type main-sequence star is converting the element hydrogen to helium in its core by means of nuclear fusion.
 The Sun, the star to which the Earth is gravitationally bound in the Solar System and the object with the largest apparent magnitude, is an example of a G-type main-sequence star.
 Each second, the Sun fuses approximately 600 million tons of hydrogen to helium, converting about 4 million tons of matter to energy.
 Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi.
Hereford Arizona Observatory (HAO), IAU-code G95, is an astronomical observatory, owned and operated by amateur astronomer Bruce L. Gary.
 Gary is the author of many publications related to astronomy, including "Exoplanet Observing for Amateurs" (2008), currently available in a second edition (2009).
 Observational studies of unusual starlight fluctuations in KIC 8462852 and WD 1145+017 are recent interests.
74 Cygni is a star in the constellation Cygnus.
 Its apparent magnitude is 5.05.
 Located around 65.83 pc distant, it is a blue-white main-sequence star of spectral type A5V, a star that is fusing its core hydrogen.
GD 61 is a white dwarf with a planetary system located 150 light-years from Earth in the constellation Perseus.
 It is thought to have been a main-sequence star of spectral type A0V with around three times the mass of the Sun that has aged and passed through a red-giant phase, leaving a dense, hot remnant that has around 70% of the Sun's mass and a surface temperature of 17,280 K.
 It is thought to be around 600 million years old, including both its life as a main-sequence star and as a white dwarf.
 It has an apparent magnitude of 14.8.
 GD 61 was first noted as a potential degenerate star in 1965, in a survey of white-dwarf suspects by astronomers from the Lowell Observatory in Arizona.
KIC 8462852 (also Tabby's Star or Boyajian's Star) is an F-type main-sequence star located in the constellation Cygnus approximately 1280 ly from Earth.
 Unusual light fluctuations of the star, including up to a 22% dimming in brightness, were discovered by citizen scientists as part of the Planet Hunters project, and, in September 2015, astronomers and citizen scientists associated with the project posted a preprint of an article describing the data and possible interpretations.
 The discovery was made from data collected by the "Kepler" space telescope, which observes changes in the brightness of distant stars to detect exoplanets.
K-type main-sequence stars may be candidates for supporting extraterrestrial life.
 These stars are known as "Goldilocks stars" as they emit enough radiation in the non-UV ray spectrum to provide a temperature that allows liquid water to exist on the surface of a planet; they also remain stable in the main phase longer than the Sun, allowing more time for life to form on a planet around a K-type main-sequence star.
 The planet's habitable zone, ranging from 0.1–0.4 to 0.3–1.3 astronomical units (AU), depending on the size of the star, is often far enough from the star so as not to be tidally locked to the star, and to have a sufficiently low solar flare activity not to be lethal to life.
 In comparison, red dwarf stars have too much solar activity and quickly tidally lock the planets in their habitable zones, making them less suitable for life.
 The odds of intelligent life arising may be better on planets around K-type main-sequence stars than around Sun-like stars, given the extra time available for it to evolve.
 Few planets thus far have been found around K-type main-sequence stars, but those that have are potential candidates for extraterrestrial life.
Iota Cygni (ι Cyg, often simply called ι Cyg) is a star in the constellation Cygnus.
 Its apparent magnitude is 3.77 Located around 37.20 pc distant, it is a blue-white main-sequence star of spectral type A5V, a star that is currently fusing its core hydrogen.
 Based on rapid changes in the strength of a singly-ionized calcium absorption line, the star is likely host to a circumstellar disk.
An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V.
 These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.
 This temperature range gives the F-type stars a yellow-white hue.
 Because a main-sequence star is referred to as a dwarf star, this class of star may also be termed a yellow-white dwarf.
 Famous examples include Procyon A, Gamma Virginis A and B, and KIC 8462852.

Question: Hereford Arizona Observatory found fluctuations in what type of main-sequence star in Cygnus?
Answer: F-type