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A Cepheid variable (/ˈsɛfɪd/ or /ˈsfɪd/) is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

A strong direct relationship between a Cepheid variable's luminosity and pulsation period established Cepheids as important indicators of cosmic benchmarks for scaling galactic and extragalactic distances. This robust characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds. This discovery allows one to know the true luminosity of a Cepheid by simply observing its pulsation period. This in turn allows one to determine the distance to the star, by comparing its known luminosity to its observed brightness.

The term Cepheid originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784, the first of its type to be so identified.

Cepheid variables are divided into two subclasses which exhibit markedly different masses, ages, and evolutionary histories: classical Cepheids and type II Cepheids. Delta Scuti variables are A class stars on or near the main sequence at the lower end of the instability strip and were originally referred to as dwarf Cepheids. RR Lyrae variables have short periods and lie on the instability strip where it crosses the horizontal branch. Delta Scuti variables and RR Lyrae variables are not generally treated with Cepheid variables although their pulsations originate with the same helium ionisation kappa mechanism.

Classical Cepheids (also known as Population I Cepheids, type I Cepheids, or Delta Cepheid variables) undergo pulsations with very regular periods on the order of days to months. Classical Cepheids are Population I variable stars which are 4–20 times more massive than the Sun, and up to 100,000 times more luminous. These Cepheids are yellow bright giants and supergiants of spectral class F6 – K2 and their radii change by (~25% for the longer-period I Carinae) millions of kilometers during a pulsation cycle.

Classical Cepheids are used to determine distances to galaxies within the Local Group and beyond, and are a means by which the Hubble constant can be established. Classical Cepheids have also been used to clarify many characteristics of our galaxy, such as the Sun's height above the galactic plane and the Galaxy's local spiral structure.

A group of classical Cepheids with small amplitudes and sinusoidal light curves are often separated out as Small Amplitude Cepheids or s-Cepheids, many of them pulsating in the first overtone.

Type II Cepheids (also termed Population II Cepheids) are population II variable stars which pulsate with periods typically between 1 and 50 days. Type II Cepheids are typically metal-poor, old (~10 Gyr), low mass objects (~half the mass of the Sun). Type II Cepheids are divided into several subgroups by period. Stars with periods between 1 and 4 days are of the BL Her subclass, 10–20 days belong to the W Virginis subclass, and stars with periods greater than 20 days belong to the RV Tauri subclass.

Type II Cepheids are used to establish the distance to the Galactic Center, globular clusters, and galaxies.

A group of pulsating stars on the instability strip have periods of less than 2 days, similar to RR Lyrae variables but with higher luminosities. Anomalous Cepheid variables have masses higher than type II Cepheids, RR Lyrae variables, and our sun. It is unclear whether they are young stars on a "turned-back" horizontal branch, blue stragglers formed through mass transfer in binary systems, or a mix of both.

A small proportion of Cepheid variables have been observed to pulsate in two modes at the same time, usually the fundamental and first overtone, occasionally the second overtone. A very small number pulsate in three modes, or an unusual combination of modes including higher overtones.

On September 10, 1784, Edward Pigott detected the variability of Eta Aquilae, the first known representative of the class of classical Cepheid variables. However, the eponymous star for classical Cepheids is Delta Cephei, discovered to be variable by John Goodricke a few months later.

A relationship between the period and luminosity for classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt in an investigation of thousands of variable stars in the Magellanic Clouds. She published it in 1912 with further evidence.

In 1913, Ejnar Hertzsprung conducted research on Cepheids. His research would later require revision, however. In 1915, Harlow Shapley used Cepheids to place initial constraints on the size and shape of the Milky Way, and of the placement of our Sun within it. In 1924, Edwin Hubble established the distance to classical Cepheid variables in the Andromeda Galaxy, until then known as the Andromeda Nebula, and showed that the variables were not members of the Milky Way. Hubble's finding settled the question raised in the "Great Debate" of whether the Milky Way represented the entire Universe or was merely one of numerous galaxies in the Universe.

In 1929, Hubble and Milton L. Humason formulated what is now known as Hubble's Law by combining Cepheid distances to several galaxies with Vesto Slipher's measurements of the speed at which those galaxies recede from us. They discovered that the Universe is expanding (see the expansion of the Universe). However, the expansion of the Universe was posited several years before by Georges Lemaître.

In the mid 20th century, significant problems with the astronomical distance scale were resolved by dividing the Cepheids into different classes with very different properties. In the 1940s, Walter Baade recognized two separate populations of Cepheids (classical and type II). Classical Cepheids are younger and more massive population I stars, whereas type II Cepheids are older fainter Population II stars. Classical Cepheids and type II Cepheids follow different period-luminosity relationships. The luminosity of type II Cepheids is, on average, less than classical Cepheids by about 1.5 magnitudes (but still brighter than RR Lyrae stars). Baade's seminal discovery led to a fourfold increase in the distance to M31, and the extragalactic distance scale. RR Lyrae stars, then known as Cluster Variables, were recognized fairly early as being a separate class of variable, due in part to their short periods.

Chief among the uncertainties tied to the classical and type II Cepheid distance scale are: the nature of the period-luminosity relation in various passbands, the impact of metallicity on both the zero-point and slope of those relations, and the effects of photometric contamination (blending) and a changing (typically unknown) extinction law on Cepheid distances. All these topics are actively debated in the literature.

These unresolved matters have resulted in cited values for the Hubble constant (established from Classical Cepheids) ranging between 60 km/s/Mpc and 80 km/s/Mpc. Resolving this discrepancy is one of the foremost problems in astronomy since the cosmological parameters of the Universe may be constrained by supplying a precise value of the Hubble constant. Uncertainties have diminished over the years, due in part to discoveries such as RS Puppis.

Delta Cephei is also of particular importance as a calibrator of the Cepheid period-luminosity relation since its distance is among the most precisely established for a Cepheid, thanks in part to its membership in a star cluster and the availability of precise Hubble Space Telescope/Hipparcos parallaxes. The accuracy of the distance measurements to Cepheid variables and other bodies within 7,500 lightyears is vastly improved by combining images from Hubble taken six months apart when the Earth and Hubble are on opposite sides of the Sun.

The accepted explanation for the pulsation of Cepheids is called the Eddington valve, or κ-mechanism, where the Greek letter κ (kappa) denotes gas opacity. Helium is the gas thought to be most active in the process. Doubly ionized helium (helium whose atoms are missing both electrons) is more opaque than singly ionized helium. The more helium is heated, the more ionized it becomes. At the dimmest part of a Cepheid's cycle, the ionized gas in the outer layers of the star is opaque, and so is heated by the star's radiation, and due to the increased temperature, begins to expand. As it expands, it cools, and so becomes less ionized and therefore more transparent, allowing the radiation to escape. Then the expansion stops, and reverses due to the star's gravitational attraction. The process then repeats.

The mechanics of the pulsation as a heat-engine was proposed in 1917 by Arthur Stanley Eddington (who wrote at length on the dynamics of Cepheids), but it was not until 1953 that S. A. Zhevakin identified ionized helium as a likely valve for the engine.

Q reports

Period Date Adjusted Actuals EPS GAAP EPS
Q4 2016 2017-01-28 Future report Set alerts
Q3 2016 2016-11-03 0.00 0.00
Q2 2016 2016-07-28 0.00 -0.14
Q1 2016 2016-04-28 0.00 -0.09
Q4 2015 2016-02-02 0.00 -0.14
Q3 2015 2015-10-20 0.00 -0.32
Q2 2015 2015-07-23 0.00 -0.23
Q1 2015 2015-04-23 0.00 0.01
Q4 2014 2015-01-29 0.00 -0.34
Q3 2014 2014-10-16 0.00 -0.10

Ratings

2016-06-29 Reiterated Rating Canaccord Genuity Hold $32.00
2016-06-15 Initiated Coverage Morgan Stanley Equal Weight $30.00
2016-04-30 Reiterated Rating Canaccord Genuity Hold
2016-04-30 Reiterated Rating Needham & Company LLC Buy
2016-04-14 Reiterated Rating Canaccord Genuity Hold $29.00 to $34.00
2016-04-01 Upgrade Atlantic Securities Neutral to Overweight
2016-04-01 Upgrade BTIG Research Neutral to Buy $42.00
2016-03-28 Lower Price Target Wedbush Outperform $58.00 to $55.00
2016-02-03 Lower Price Target Robert W. Baird Outperform $45.00 to $40.00
2016-02-03 Lower Price Target Stifel Nicolaus Buy $42.00 to $38.00
2016-02-03 Reiterated Rating Canaccord Genuity Hold $34.00 to $29.00
2016-02-03 Lower Price Target Barclays Equal Weight $38.00 to $36.00
2016-02-03 Reiterated Rating Leerink Swann Market Perform $39.00 to $33.00
2016-02-03 Reiterated Rating Needham & Company LLC Buy $44.00
2016-02-03 Reiterated Rating BTIG Research Neutral
2016-02-03 Reiterated Rating Cowen and Company Buy
2016-02-03 Lower Price Target Barclays PLC Equal Weight $38.00 to $36.00
2016-01-07 Boost Price Target Cowen and Company $40.00
2016-01-07 Lower Price Target Barclays Equal Weight $40.00 to $38.00
2016-01-06 Initiated Coverage Avondale Partners Outperform $46.00
2015-12-17 Upgrade Needham & Company LLC Hold to Buy $44.00
2015-12-03 Reiterated Rating Canaccord Genuity Hold $34.00
2015-12-02 Downgrade Canaccord Genuity Hold to Market Perform $42.41 to $42.21
2015-12-02 Downgrade Wells Fargo Outperform to Market Perform
2015-12-02 Downgrade Wells Fargo & Co. Outperform to Market Perform
2015-12-01 Reiterated Rating BTIG Research Neutral
2015-12-01 Downgrade Needham & Company LLC Hold
2015-11-12 Initiated Coverage Stifel Nicolaus Buy $42.00
2015-10-21 Reiterated Rating BTIG Research Neutral
2015-10-21 Lower Price Target Wedbush Outperform $55.00 to $54.00
2015-10-21 Reiterated Rating Leerink Swann Market Perform $44.00 to $39.00
2015-10-21 Lower Price Target Craig Hallum Buy $52.00 to $42.00
2015-10-21 Lower Price Target Cowen and Company $42.00 to $38.00
2015-10-21 Upgrade Evercore ISI Sell to Hold $44.50 to $32.50
2015-10-21 Downgrade Needham & Company LLC Buy to Hold
2015-10-21 Downgrade Canaccord Genuity Buy to Hold $42.00 to $34.00
2015-10-21 Lower Price Target Mizuho Buy $60.00 to $42.00
2015-10-15 Lower Price Target Citigroup Inc. Buy $62.00 to $48.00
2015-10-15 Reiterated Rating Canaccord Genuity Buy $42.00
2015-10-15 Reiterated Rating BTIG Research Neutral
2015-10-14 Reiterated Rating Piper Jaffray Buy $66.00 to $62.00
2015-10-14 Lower Price Target Wedbush Outperform $66.00 to $55.00
2015-10-14 Lower Price Target Leerink Swann Market Perform $58.00 to $44.00
2015-10-14 Lower Price Target Jefferies Group Hold $55.00 to $35.00
2015-10-14 Lower Price Target Goldman Sachs $53.00 to $30.00
2015-10-14 Lower Price Target Craig Hallum Buy $75.00 to $52.00
2015-10-14 Lower Price Target Cowen and Company Outperform $64.00 to $42.00
2015-10-14 Lower Price Target Barclays Equal Weight $55.00 to $40.00
2015-10-14 Lower Price Target Needham & Company LLC Buy $70.00 to $47.00
2015-10-14 Downgrade Raymond James Outperform to Market Perform
2015-10-14 Reiterated Rating Piper Jaffray Cos. Buy $66.00 to $62.00
2015-10-14 Lower Price Target Goldman Sachs Group Inc. $53.00 to $30.00
2015-10-14 Downgrade Raymond James Financial Inc. Outperform to Market Perform
2015-09-02 Initiated Coverage Barclays Equal Weight $55.00
2015-08-14 Reiterated Rating Mizuho Buy $72.00 to $60.00
2015-08-14 Reiterated Rating Canaccord Genuity Buy $68.00
2015-07-26 Reiterated Rating MKM Partners Buy $65.00 to $72.00
2015-07-25 Reiterated Rating Wedbush Buy
2015-07-24 Reiterated Rating Canaccord Genuity Buy $68.00
2015-07-24 Lower Price Target Wedbush Outperform $67.00 to $66.00
2015-07-24 Reiterated Rating Evercore Partners Inc. Hold to Sell
2015-07-24 Boost Price Target Needham & Company LLC Buy $66.00 to $70.00
2015-07-24 Boost Price Target Mizuho Buy $65.00 to $72.00
2015-07-24 Downgrade Evercore ISI Hold to Sell $53.50
2015-07-23 Reiterated Rating BTIG Research Hold
2015-06-26 Upgrade Craig Hallum Hold to Buy $52.00 to $75.00
2015-05-20 Boost Price Target Canaccord Genuity Buy $66.00 to $68.00
2015-04-26 Reiterated Rating BTIG Research Neutral
2015-04-26 Reiterated Rating Cantor Fitzgerald Buy $62.00
2015-04-26 Reiterated Rating Canaccord Genuity Buy $66.00
2015-04-24 Boost Price Target JMP Securities Market Outperform $58.00 to $67.00
2015-04-24 Boost Price Target Needham & Company LLC Buy $61.00 to $66.00
2015-04-08 Reiterated Rating Canaccord Genuity Buy $65.00
2015-01-30 Boost Price Target Oppenheimer Outperform $57.00 to $60.00
2015-01-30 Reiterated Rating BTIG Research Neutral
2015-01-30 Boost Price Target Oppenheimer Holdings Inc. Outperform $57.00 to $60.00
2015-01-05 Reiterated Rating BTIG Research Neutral
2014-12-30 Reiterated Rating William Blair Buy
2014-12-30 Upgrade Bank of America Neutral to Buy
2014-12-30 Upgrade Bank of America Corp. Neutral to Buy
2014-12-18 Upgrade Bank of America Neutral to Buy $56.00 to $60.00
2014-12-04 Reiterated Rating Citigroup Inc. Buy $52.00 to $62.00
2014-12-03 Initiated Coverage BTIG Research Neutral
2014-12-02 Boost Price Target Oppenheimer Outperform $54.00 to $57.00
2014-10-17 Reiterated ISI Group Neutral $43.50 to $45.50
2014-10-17 Boost Price Target Evercore ISI Neutral $43.50 to $45.50
2014-10-09 Initiated Coverage Citigroup Inc. Buy
2014-09-17 Upgrade Cantor Fitzgerald Hold to Buy $52.00
2014-08-11 Upgrade ISI Group Sell to Neutral $38.50
2014-08-11 Boost Price Target S&P Equity Research Average to Hold $6.58 to $8.30
2014-08-11 Upgrade Evercore ISI Sell to Neutral $38.50
2014-07-18 Reiterated Needham Buy $50 to $52
2014-07-18 Reiterated Rating Raymond James Outperform $57.00 to $54.00
2014-07-18 Lower Price Target Evercore ISI $37.00
2014-07-18 Boost Price Target Needham & Company LLC Buy $50.00 to $52.00
2014-07-10 Reiterated Rating Cowen and Company Outperform $62.00 to $58.00
2014-07-09 Initiated Coverage Wells Fargo & Co. Outperform
2014-07-09 Initiated Coverage Wells Fargo Outperform
2014-06-09 Upgrade Craig Hallum Sell to Hold
2014-06-09 Reiterated Rating SunTrust Neutral $54.00 to $49.00
2014-05-27 Upgrade Needham Hold to Buy $50
2014-05-27 Upgrade Needham & Company LLC Hold to Buy $50.00
2014-04-28 Upgrade Ned Davis Research Sell to Neutral
2014-04-21 Reiterated Rating SunTrust Neutral $59.00 to $54.00
2014-04-21 Boost Price Target Jefferies Group Hold $43.00 to $44.00
2014-04-09 Upgrade JMP Securities Market Perform to Outperform $58.00
2014-04-02 Boost Price Target Canaccord Genuity $55.00 to $62.00
2014-03-10 Boost Price Target Cowen and Company $53.00 to $62.00
2014-01-31 Boost Price Target Mizuho Buy $50.00 to $65.00
2014-01-31 Boost Price Target Jefferies Group $36.00 to $43.00
2014-01-31 Boost Price Target Raymond James $50.00 to $57.00
2014-01-31 Boost Price Target Oppenheimer $43.00 to $54.00
2014-01-31 Boost Price Target Evercore ISI $38.00 to $39.00
2014-01-31 Boost Price Target Cowen and Company $52.00 to $53.00
2014-01-31 Boost Price Target Citigroup Inc. $48.00 to $53.00
2014-01-31 Boost Price Target Canaccord Genuity Buy $50.00 to $55.00
2014-01-07 Downgrade JPMorgan Chase & Co. Overweight to Neutral
2013-12-19 Initiated Needham Hold
2013-12-19 Initiated Coverage Needham & Company LLC Hold
2013-12-18 Initiated Coverage JMP Securities Market Perform
2013-11-22 Boost Price Target Raymond James Buy $43.00 to $50.00
2013-11-20 Set Price Target Wedbush Outperform $42.00 to $47.00
2013-10-28 Boost Price Target Cowen and Company Outperform $42.00 to $44.00
2013-10-18 Boost Price Target Mizuho Buy $42.00 to $50.00
2013-10-18 Reiterated Rating Wedbush Buy $42.00
2013-10-18 Lower Price Target Evercore ISI Sell $34.00 to $33.50
2013-10-18 Boost Price Target Canaccord Genuity Buy $45.00 to $50.00
2013-10-10 Initiated Coverage SunTrust Neutral
2013-10-04 Downgrade ISI Group Cautious to Sell
2013-10-03 Boost Price Target Wedbush Outperform $37.00 to $42.00
2013-10-01 Downgrade Bank of America Buy to Neutral $39.00 to $41.00
2013-06-26 Resumed Oppenheimer Outperform $41
2013-04-19 Reiterated Mizuho Buy $37 to $42
2012-10-19 Reiterated ISI Group Sell $30.50 to $29
2012-09-27 Reiterated ISI Group Sell $35 to $32.50
2012-08-30 Initiated Cantor Fitzgerald Hold $40
2012-05-14 Downgrade GARP Research Buy to Neutral
2016-06-29 Reiterated Rating Canaccord Genuity Hold $32.00
2016-06-15 Initiated Coverage Morgan Stanley Equal Weight $30.00
2016-04-30 Reiterated Rating Canaccord Genuity Hold
2016-04-30 Reiterated Rating Needham & Company LLC Buy
2016-04-14 Reiterated Rating Canaccord Genuity Hold $29.00 to $34.00

There is presents forecasts of rating agencies and recommendations for investors about this ticker

Major Shareholders

Name Relationship Total Shares Holding stocks
KEPNER CRISTINA 0.39%  (274404) CPHD /
GUTSHALL THOMAS L 0.15%  (106959) CPHD /
BISHOP JOHN L Chairman of the Board and CEO 0.12%  (82596) CPHD / VCYT /
Brown Thomas D 0.07%  (51876) AXDX / CPHD / QDEL / SRCL /
Murray Bill EVP, General Counsel 0.04%  (31063) CPHD /
SMITH JOSEPH H EVP, Bus Dev and GC 0.04%  (26669) CPHD /
KOCMOND WARREN C JR EVP, Global Operations 0.04%  (25420) CPHD /
Haugen Marc EVP, Global Ops & Engineering 0.03%  (20000) CPHD /
Farrell Peter V. EVP, Int\'l Commercial Ops 0.03%  (19323) CPHD /
MORTON DEAN O 0.03%  (18134) CPHD /
Fitzgerald Mike EVP, Global Human Resources 0.03%  (17904) CPHD / ZLTQ /
RENTON HOLLINGS 0.02%  (14917) AFFY / CPHD / KYTH / PTLA / RIGL /
STEELE GLENN JR MD PHD 0.02%  (14677) CPHD / PTCT / WCG /
PERSING DAVID H Exec VP,Chief Med/Tech Officer 0.02%  (14175) CPHD /
EASTON ROBERT J 0.02%  (12844) CPHD /
Campbell Scott A. VP, Clinical Affairs & CRO 0.01%  (10089) CPHD /
Daskal Ilan EVP, Chief Financial Officer 0.01%  (10000) CPHD / IRF / SUNE / XXIA /
Madden Dan EVP, Chief Financial Officer 0.01%  (9898) CPHD /
Paterson Wayne 0.01%  (4500) CPHD /

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